The best starting point in my experience is https://regolith-desktop.com. You install it and get a noob-friendly, pre-configured unixporn desktop out of the box.
Once you start using it, the rest of the obscure programs referenced on /r/unixporn start making sense too.
You don't need navidrome!
Can't help with the mpv thing unfortunately. I just selected browser audio as the backend.
You could check the issue tracker though.