This is mostly configuration of my personal Raspberry Pi, which I happen to do
using NixOS. So if you're also interested in running NixOS on your Raspberry,
start looking around starting at sd-image-homepi.nix.
There's one file secrets.nix which includes Wifi credentials and password
hashes and hence are a) likely not of interest anyways and b) private.
I'm running this on a Raspberry Pi 3B+
To build the SD image, simply run nix-build like so:
nix-build '<nixpkgs/nixos>' -A config.system.build.sdImage --argstr system aarch64-linux -I nixos-config=./sd-image-homepi.nix -I nixpkgs=https://releases.nixos.org/nixos/20.03/nixos-20.03beta-475.71be729a58e/nixexprs.tar.xz -o result-homepi
Of course your local machine needs to be able to compile/run aarch64-linux binaries.
If you happen to see Cannot allocate memory error messages emitted by cptofs,
simply ignore them. It seems to do its job just fine anyways.
PS: make sure to use NixOS 20.03 (or later); former versions like 19.09 seem to cause trouble (at least it does not successfully run the system activation script on first boot).