Well, I've maintained my music collection from the olden days, and acquire new music as I discover I like it. I mostly have trash vaporwave tastes so I actually buy most of my music cheaply on bandcamp. My music collection isn't massive like some peoples, but it's a decent amount of GB. Mostly mp3, I'm not fancy enough for FLAC.
As for hosting the music, check out Navidrome. It's a great subsonic compatible service that can run on your OS of choice. I use Symfonium on Android to access the library. It supports playlist syncing, offline caching, etc. etc.