diff --git a/tools/install-monorepo.sh b/tools/install-monorepo.sh
index 4faaec56ac4b2..17763456f68a6 100755
--- a/tools/install-monorepo.sh
+++ b/tools/install-monorepo.sh
@@ -1,9 +1,11 @@
 #!/usr/bin/env bash
-
 set -eo pipefail
 
-BASE=$(cd $(dirname "${BASH_SOURCE[0]}")/.. && pwd)
-source "$BASE/tools/includes/chalk-lite.sh"
+# Start in the monorepo root folder.
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+# Source some helper functions.
+source tools/includes/chalk-lite.sh
 
 # Print help and exit.
 function usage {
@@ -15,143 +17,304 @@ function usage {
 	exit 1
 }
 
-if [[ $1 ]]; then
-	usage
-fi
+# Wrapper to check for a command silently.
+#
+# $1 - Command to check for
+# Returns: 0 if the command exists, non-zero if not.
+function has_command {
+	command -v "$1" &>/dev/null
+	return $?
+}
 
-# Check if we're on a Mac or Linux, bail if we're not.
-OS="$(uname)"
-if [[ "$OS" == "Linux" ]]; then
-	ON_LINUX=1
-	if ! command -v apt &>/dev/null; then
-		die "Installer script requires 'apt' to ensure essentials are installed."
+# Check if we're on macOS; bail if we're not.
+function do_system {
+	if [[ "$(uname)" != "Darwin" ]]; then
+		die "Installer script is only supported on macOS."
 	fi
-	sudo apt update
-	sudo apt install build-essential
-elif [[ "$OS" != "Darwin" ]]; then
-	die "Installer script is only supported on macOS and Linux."
-fi
+	echo "Valid OS: macOS (Darwin)"
+}
 
-# Check for curl and git
-if ! command -v git &>/dev/null; then
-	die "Installer script requires 'git' to be installed."
-fi
+# Checks for git and curl.
+function do_basics {
 
-if ! command -v curl &>/dev/null; then
-	die "Installer script requires 'curl' to be installed"
-fi
+	# Check for curl and git
+	if ! has_command git; then
+		echo "git: not found"
+		die "Installer script requires git to be installed."
+	fi
+	echo "git: available"
 
-# Check of Homebrew and nvm are installed
-info "Checking if Homebrew is installed..."
-if ! command -v brew &>/dev/null; then
-	info "Installing Homebrew"
-	/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
-	if [[ -n "$ON_LINUX" ]]; then # Add homebrew to PATH
-		echo 'eval "$("/home/linuxbrew/.linuxbrew/bin/brew" shellenv)"' >> "$HOME/.profile"
-		eval "$("/home/linuxbrew/.linuxbrew/bin/brew" shellenv)"
-		PATH="/home/linuxbrew/.linuxbrew/bin:$PATH"
+	if ! has_command curl; then
+		echo "curl: not found"
+		die "Installer script requires curl to be installed."
 	fi
-else
-	info "Updating brew"
-	brew update
-	# Brew can be finicky on MacOS
-	if [[ $? -ne 0 ]]; then
-		 echo "Reinstalling Homebrew"
-		 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
+	echo "curl: available"
+}
+
+# Checks for, installs, and updates Homebrew.
+function do_homebrew {
+	if ! has_command brew; then
+		echo "brew: not found"
+		echo "Installing brew..."
+		/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" || die "Unable to install brew!"
+		HOMEBREW_PREFIX="/opt/homebrew"
+
+		# Add brew env to current script for use later.
+		eval "$(${HOMEBREW_PREFIX}/bin/brew shellenv)"
+
+		if ! has_command brew; then
+			die "Unable to install brew!"
+		fi
+		echo "Installed brew."
+
+		# Determine shell RC file.
+		# Adapted from Homebrew install script:
+		# https://github.com/Homebrew/install/blob/master/install.sh
+		case "${SHELL}" in
+			*/bash*)
+				shell_rcfile="${HOME}/.bash_profile"
+				;;
+			*/zsh*)
+				shell_rcfile="${ZDOTDIR:-"${HOME}"}/.zprofile"
+				;;
+			*/fish*)
+				shell_rcfile="${HOME}/.config/fish/config.fish"
+				;;
+			*)
+				shell_rcfile="${ENV:-"${HOME}/.profile"}"
+				;;
+		esac
+
+		# Add brew init to shell rc file.
+		if ! grep -qs "eval \"\$(${HOMEBREW_PREFIX}/bin/brew shellenv)\"" "${shell_rcfile}"; then
+			(echo; echo "eval \"\$(${HOMEBREW_PREFIX}/bin/brew shellenv)\"") >> "${shell_rcfile}"
+		fi
+
+	else
+		# Run brew updates
+		if ! brew update &> /dev/null; then
+			die "Unable to update brew!"
+		fi
 	fi
-fi
+	export HOMEBREW_NO_AUTO_UPDATE=1
+	export HOMEBREW_NO_ENV_HINTS=1
+	echo "brew: available"
+}
 
-info "Checking if NVM is installed..."
-if ! command -v nvm &>/dev/null; then
-	info "Installing nvm"
-	curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash && export NVM_DIR=$HOME/.nvm && source $NVM_DIR/nvm.sh  --no-use
-else
-	info "Updating nvm"
-	curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash
-fi
+# Checks for, installs, and updates nvm.
+function do_nvm {
+	# Get latest nvm version.
+	# Based on this: https://stackoverflow.com/a/71896712
+	local good_nvm_version=$(basename "$(curl -fs -o/dev/null -w '%{redirect_url}' https://github.com/nvm-sh/nvm/releases/latest)")
+
+	if [[ -f "$HOME"/.nvm/nvm.sh ]] ; then
+		# Since nvm is really several shell functions, and isn't in the environment
+		# initially, we need to source it.
+		if [[ -f "$(brew --prefix nvm)/nvm.sh" ]]; then
+			# Sometimes nvm is installed via brew, which is an unsupported install
+			# route, and uses a wrapper helper script.
+			source "$(brew --prefix nvm)/nvm.sh"
+		else
+			export NVM_DIR="$HOME/.nvm" && source "$NVM_DIR"/nvm.sh --no-use
+		fi
 
-# Install and use the correct version of Node.js
-info "Installing Node.js"
-nvm install && nvm use
+		if [[ v$(nvm --version) != "$good_nvm_version" ]]; then
+			echo "nvm: wrong version"
+			echo "Updating nvm..."
 
-# Install our requirements
-info "Checking Bash version..."
-if [[ -z "${BASH_VERSINFO}" || -z "${BASH_VERSINFO[0]}" || ${BASH_VERSINFO[0]} -lt 4 ]]; then
-	brew install bash
-fi
+			# Download latest version
+			curl -s -o- "https://raw.githubusercontent.com/nvm-sh/nvm/$good_nvm_version/install.sh" | bash - &>/dev/null &&
 
-info "Checking if jq is installed..."
-if ! command -v jq &>/dev/null; then
-	info "Installing jq"
-	brew install jq
-fi
+			# Source again to get latest shell functions
+			source "$NVM_DIR/nvm.sh" --no-use
 
-info "Checking if pnpm is installed..."
-if ! command -v pnpm &>/dev/null; then
-	info "Installing pnpm"
-	# Don't use https://get.pnpm.io/install.sh, that doesn't play nice with different shells.
-	# And corepack will likely lose pnpm every time nvm installs a new node version.
-	curl -f https://get.pnpm.io/v6.16.js | node - add --global pnpm
-fi
-if [[ -z "$( pnpm bin --global )" ]]; then
-	info "Setting up pnpm"
-	if ! pnpm setup; then
-		warn 'pnpm has no bin dir set, and `pnpm setup` failed. Linking the Jetpack CLI may fail.'
+			# Something's wrong, so abort.
+			if [[ "v$(nvm --version)" != "$good_nvm_version" ]]; then
+				die "Unable to update nvm!"
+			fi
+			echo "Updated nvm."
+		fi
 	else
-		# Try to read PNPM_HOME from the login shell after `pnpm setup`, as pnpm probably changed it.
-		P=$( "$SHELL" -i -c 'echo $PNPM_HOME' ) || true
-		if [[ -n "$P" ]]; then
-			export PNPM_HOME="$P"
-			if [[ ":$PATH:" != *":$PNPM_HOME:"* ]]; then
-				export PATH="$PNPM_HOME:$PATH"
+		echo "nvm: not found"
+		info "Installing nvm..."
+		curl -s -o- "https://raw.githubusercontent.com/nvm-sh/nvm/$good_nvm_version/install.sh" | bash - &>/dev/null &&
+
+		# Source to get latest shell functions
+		export NVM_DIR="$HOME"/.nvm && source "$NVM_DIR"/nvm.sh --no-use
+
+		# Something's wrong, so abort.
+		if ! has_command nvm; then
+			die "Unable to install nvm!"
+		fi
+		echo "Installed nvm."
+	fi
+
+	echo "nvm: available"
+}
+
+# Checks for and installs node.
+function do_node {
+	good_node_version=$(cat .nvmrc)
+	if ! has_command node; then
+		echo "node: not found"
+		echo "Installing node..."
+		nvm install
+		# Something's wrong, so abort.
+		if ! has_command node; then
+			die "Unable to install node!"
+		fi
+		echo "Node installed."
+	elif [[ $(node --version) != v"$good_node_version" ]]; then
+		# Install correct version if not yet installed
+		if ! nvm list node | grep -q "$good_node_version"; then
+			echo "node: needed version not installed"
+			echo "Installing correct node version..."
+			nvm install
+			# Something's wrong, so abort.
+			if ! nvm list node | grep -q "$good_node_version"; then
+				die "Unable to install needed version of node!"
 			fi
+			echo "Correct version of node installed."
 		fi
 	fi
-fi
+	# Switch node version
+	nvm use &> /dev/null
+	echo "node: available"
+}
 
-source .github/versions.sh
-info "Installing and linking PHP $PHP_VERSION"
-brew install php@$PHP_VERSION
-brew link php@$PHP_VERSION
-
-info "Checking composer..."
-if ! command -v composer &>/dev/null; then
-	info "Installing Composer"
-	EXPECTED_CHECKSUM="$(php -r 'copy("https://composer.github.io/installer.sig", "php://stdout");')"
-	php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
-	ACTUAL_CHECKSUM="$(php -r "echo hash_file('sha384', 'composer-setup.php');")"
-
-	if [[ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]]; then
+function do_bash {
+	if [[ -z "${BASH_VERSINFO}" || -z "${BASH_VERSINFO[0]}" || ${BASH_VERSINFO[0]} -lt 4 ]]; then
+		echo "bash 4+: not found"
+		echo "Installing bash..."
+		brew install bash
+		if [[ -z "${BASH_VERSINFO}" || -z "${BASH_VERSINFO[0]}" || ${BASH_VERSINFO[0]} -lt 4 ]]; then
+			die "Unable to install newer version of 'bash'!"
+		fi
+		echo "Installed bash."
+	fi
+	echo "bash 4+: available"
+}
+
+function do_jq {
+	if ! has_command jq; then
+		echo "jq: not found"
+		echo "Installing jq..."
+		brew install jq &>/dev/null
+		if ! has_command jq; then
+			die "Unable to install jq!"
+		fi
+		echo "Installed jq."
+	fi
+	echo "jq: available"
+}
+
+function do_pnpm {
+	if ! has_command pnpm; then
+		echo "pnpm: not found"
+		echo "Installing pnpm..."
+		curl -fsSL https://get.pnpm.io/install.sh | env PNPM_VERSION="$PNPM_VERSION" sh - &>/dev/null
+
+		# Make sure pnpm is in one's path
+		export PNPM_HOME="$("$SHELL" -i -c 'echo "$PNPM_HOME"')"
+		export PATH="$("$SHELL" -i -c 'echo "$PATH"')"
+		if ! has_command pnpm; then
+			die "Unable to install 'pnpm'!"
+		fi
+		echo "Installed pnpm."
+	fi
+	echo "pnpm: available"
+}
+
+function do_php {
+	if ! has_command php || php -r "exit( version_compare( PHP_VERSION, '$PHP_VERSION', '<' ) ? 0 : 1 );"; then
+		echo "PHP $PHP_VERSION: not found"
+
+		# Note that we can't use grep -q, as it's prematurely terminated.
+		if ! $(brew list|grep php@$PHP_VERSION >/dev/null); then
+			echo "Installing PHP $PHP_VERSION..."
+			# Don't hide output, as this can take some time...
+			brew install php@"$PHP_VERSION"
+		else
+			echo "Linking already-installed PHP $PHP_VERSION..."
+		fi
+		brew link --overwrite php@"$PHP_VERSION" &>/dev/null
+		if ! has_command php || php -r "exit( version_compare( PHP_VERSION, '$PHP_VERSION', '<' ) ? 0 : 1 );"; then
+			die "Unable to install PHP $PHP_VERSION!"
+		fi
+	fi
+	echo "PHP $PHP_VERSION: available"
+}
+
+function do_composer {
+	if ! has_command composer; then
+		echo "composer: not found"
+		echo "Installing composer..."
+
+		# Note that installing from brew adds various unneeded dependencies (e.g. extra PHP).
+		# Largely grabbed from official install script:
+		# https://getcomposer.org/doc/faqs/how-to-install-composer-programmatically.md
+		EXPECTED_CHECKSUM="$(php -r 'copy("https://composer.github.io/installer.sig", "php://stdout");')"
+		php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
+		ACTUAL_CHECKSUM="$(php -r "echo hash_file('sha384', 'composer-setup.php');")"
+
+		if [[ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]]; then
+			rm composer-setup.php
+			die "Invalid composer installer checksum!"
+		fi
+
+		php composer-setup.php --quiet --version="$COMPOSER_VERSION"
+		RESULT=$?
 		rm composer-setup.php
-		die 'ERROR: Invalid composer installer checksum'
+		if [[ $RESULT -ne 0 ]]; then
+			die "Unable to install composer!"
+			if [[ -f composer.phar ]]; then
+				# Clean up.
+				rm composer.phar
+			fi
+		fi
+		sudo mkdir -p /usr/local/bin
+		sudo mv composer.phar /usr/local/bin/composer
+		if ! has_command composer; then
+			die "Unable to install composer!"
+		fi
+		echo "Installed composer."
 	fi
+	echo "composer: available"
+}
 
-	php composer-setup.php --version=$COMPOSER_VERSION --quiet
-	RESULT=$?
-	rm composer-setup.php
-	sudo mkdir -p /usr/local/bin
-	sudo mv composer.phar /usr/local/bin/composer
-fi
+function do_monorepo_config {
+	echo "Setting up the Jetpack monorepo tooling..."
+	pnpm install
+	composer install
+	pnpm jetpack cli link &>/dev/null
+	if ! command -v jetpack &>/dev/null; then
+		warn 'Failed to link Jetpack CLI. The `jetpack` command will be unavailable.'
+		warn 'You can still use `pnpm jetpack` or set up an alias as desired.'
+	fi
+}
 
-# Setup the Jetpack CLI
-info "Setting up the Jetpack CLI"
-pnpm install
-pnpm jetpack cli link
-if ! command -v jetpack &>/dev/null; then
-	warn 'Failed to link Jetpack CLI. The `jetpack` command will be unavailable.'
-	warn 'Likely this is because `pnpm setup` has not been run successfully. You may use `pnpm jetpack` from within the monorepo checkout instead.'
-fi
-pnpm jetpack install --root
-
-success "Installation complete. You may need to restart your terminal for changes to take effect. Then you can run tools/check-development-environment.sh to make sure everything installed correctly."
-
-# Reset the terminal so it picks up the changes.
-if [[ "$SHELL" == "/bin/zsh" ]]; then
-	info "Refreshing terminal"
-	exec zsh
-elif [[ "$SHELL" == "/bin/bash" ]]; then
-	info "Refreshing terminal"
-	exec bash
-else
-	info "Note: You may have to restart your terminal for monorepo tools to work properly."
+if [[ $1 ]]; then
+	usage
 fi
+
+do_system
+do_basics
+do_homebrew
+do_nvm
+do_node
+do_bash
+do_jq
+
+# Get repo-preferred versions
+source .github/versions.sh
+do_pnpm
+do_php
+do_composer
+
+echo
+do_monorepo_config
+
+echo
+echo "Installation complete. You will need to restart your terminal for changes"
+echo "to take effect. You can then run ./tools/check-development-environment.sh"
+echo "to make sure everything installed correctly."