Not sure whether timeshift supports multiple systems per partition, but I’d be very surprised if you couldn’t create separate partitions for each PC

They provide .deb files. I didn’t hunt any further than that

You will be fine. I game on mint with an Nvidia card. Steam has a setting to fall back to proton for all games without native Linux, and for everything off steam use Lutris (install it from the website, since the package manager version is too old to be useful)

Which one?

WE DO NOT BREAK USERSPACE

For all Spotify’s failings, this is something it actually does a great job at. I get a playlist of new recommendations each week, 6+ daily playlists in different styles, playlists based on artists/genres/moods etc.

Plus the cost of your own ram, storage, etc.

USB flash drive