I used to just torrent music directly to my phone so I could use a good local app, but I’ve gone down the subsonic route, bc it is pretty slick.

• Torrent / however you get music, put it in a folder on a server.
• Install Navidrome, point it at your music folder.
• Get DSub for android, a great player that can even work with chromecast, can cache music locally, create playlists, etc.