A simple Python script for launching Minecraft. You could use it as a template to make custom Minecraft launchers for modpacks and stuff. You might find it useful. Do what you want. It's on the BSD license.
They are in the mcdata folder that this scripts creates instead of the normal .minecraft folder.
Yes, but when installing Forge, you must direct it to the mcdata folder isntead of the default .minecraft. Also, the multi-modpack support must be able to create symlinks/shortcuts called config and mods, so instead of putting your mods and config into those folders, rename them to mods-single and config-single, and MaddCraft will automatically create the appropriate links to direct Forge to them. You may also have other mods and config folders, when using MaddCraft modpack servers.