It’s DRM free, you can download it with heroic, copy the files and then delete your epic account

Stremio Youtube

You can use pretty much anything you can with desktop Linux, however some apps may not work with a controller

Jellyfin is quite capable for music, however Navidrome has a much better client ecosystem. Personally I use the Finamp beta on mobile as it does everything I want and is quite stable, but if you want Android auto/apple carplay you will have to use a client that isn’t as reliable or proprietary (paid.