The metadata proxy that mirrors musicbrainz DB is broken (read: Imploded).
For now artist/album search is broken.
Dunno about metadata-tagging for existing entries

Yeah, it does a good enough job of handling the metadata which is why I mentioned it. To find books you need a private tracker.

Zotify and similar tools (not those youtube downloaders!)

They're kind of small enough that if I want a PDF, I can just google it and download it from some random foreign university who are hosting it for some reason. You'd likely struggle to find more obscure stuff that way though.

yes that is correct. it is a server/client solution so you can track you progress.

zero finding ability. try Lazy Librarian.

remember that audiobooks are relatively rare due to their high production costs. so a lot of books do not have an audio version. Could consider text to speech.

there are some massive torrents that have like thousands of audiobooks in them and you have to go and select which ones to download. I'm not sure how I stumbled on these in the past so if you figure that out let me know.

The best way I found to do this was using audiobookshelfs upload feature and grabbing the meta data before upload. This sorts the folders for you

It's sort of weird to upload because it's already on the hard drive where I want it to go.. Just has to get squeezed back and forth through the pipes of my LAN a few times to go through this process.

Yeah it's not perfect. I normally just download and upload from my phone so works for me but it's not a very automated or neat solution but it does work and uploads don't take to long