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. :)
It’s possible for a certain hardware/software setup not to support a certain codec. For example, my jellyfin client (Finamp) uses the iOS native decoders (afaik), which means opus files are practically broken. My music library (8000+ songs) contained exactly 1 lossy file, which just so happened to be an opus file. I decided to spend the extra ~20MB to standardise my entire library to flac files, ensuring I could play every song on all my devices.
Edit cause I posted too soon: you are generally correct; only in very specific circumstances will you encounter compatibility issues like this one in the modern world. This is 100% apple being apple, and you can expect pretty much every other (reasonably modern) device to support all codecs you might encounter in the wild.