3

I use TrackerControl for trackers in apps (and as others said Firefox+uBO, NewPipe for Youtube)

I ended up installing Syncthing using Termux following these instructions: https://www.stephenjianu.com/syncthing-android/

Yes

I like Amperfy and I think Navidrome has a Subsonic API: https://github.com/BLeeEZ/amperfy