No deemix only picks from deezer, but It seems to have song parity with spotify. Or rather I haven’t found a song on spotify that wasn’t in deezer.
As far as metadata, I use picard to autopopulate meta data from musicbrainz. My typical workflow is find something in deemix, download it and put it in a staging directory, then have lidarr import, trackname fix, and metadata fix, and then finally have navidrome scan the final folder and make the music accessible.
So as you noticed there isn’t a one size fits all solution.
You are correct in that bandcamp allows you to buy songs and albums from artists, but not every artist is on the platform. I cycle between Quobuz, HDTracks, or other alternatives (wink, wink)
Navidrome is good for sharing one library, in my experience. It expects one library that a bunch of users can then interact with. This does meet your requirements of seperate stats and downloads per user however you will have access to your family’s music just like they will have access to yours.
You could try out funkwhale, which is similar but expects multiple libraries. So you can have a library of just your music and same with your family members, this will allow duplicate tracks. I will caution that funkwhale is, in my experience, not easy to get setup. I would personally recommend navidrome as it is very easy to setup annd use. As others mentioned, it uses the subsonic api under the hood so any subsonic client can access your navidrome libary. I use Feishen on desktop and symphonium on mobile.
You also mention syncing music folders between devices, this might get tricky. But you can setup a rsync services to ssh to your phone and then migrate tracks to your library. But personally I would recommend just trying to only download your music to your NAS so you can skip this annoyance. You can setup Lidarr which is sonarr/radarr but for music. However music piracy is not what it was 10 years ago, and I struggle to have lidarr autopull albums, but thats also because I try to use flac which is not as common either.
Finally you mention recommendations, for me the only option is ListenBrainz. You can setup a musicbrainz account, it is an open source music metadata platform, and then use that login for ListenBrainz, which is a tracking and recommendation engine. You can directly plug in that api to navidrome to have it sync all of your listens.
In summary, my recommendation is to only download music to your nas, setup navidrome for library sharing, (you can download from navidrome), and then setup lidarr for albums. Finally for individual tracks look into deemix, if you only want mp3 then it’s just free downloads.
Please feel free to reply or message for any clarifications.
I’m ashamed to admit I never considered hooking deemix into lidarr, that is pure genious.
I’d also second collecting whole discographies, a lot of ‘one hit wonders’ have surprisingly deep catalogs that are full of really great tunes.