Do I use a website to download songs off of YouTube or Spotify?
Where should I store the music? I haven't any clue about self-hosting. I'm running GrapheneOS, is it enough to save the songs in Files and play in an app like Auxio? Maybe sync with SyncThing?
What's the best way to compress mp3 files but still retain the quality (even possible)?
Could really use some help as I'm very inexperienced. :)
If you're not starting from a lossless format (like FLAC), you shouldn't really be compressing anything. When compressing from a lossless format to MP3, it's totally subjective. When I was more into ripping CDs, I'd do V0 or 320 - there's probably plenty of internet arguments by people more knowledgeable than me if you need a breakdown in different MP3 compressions.