I really like Spotify but I feel I'm soon going to rebuild an MP3 library. A mix of songs being removed (licensing), the apps being sluggish due to library size and local playlist features being rubbish for years. I've got enough "niche" read: game osts and that to make it worth while.
For anyone considering the same, beets (python) is your best friend
I prefer using Quod Libet. It does take a bit of customizing, but the benefit is that you can customize everything. It also doesn't try to do anything fancy with tags, letting you determine the entire structure you want to use, including custom tags.
It's the only credible alternative to Foobar2000 on Linux.
This is why I like Apple Music. If an album I want isn’t available for streaming I can just buy it. I can also buy music that Apple doesn’t carry (from Beaport for example) and add it to my library and play everything whether streaming, bought through Apple or other services in a single place.
For anyone considering the same, beets (python) is your best friend