For downloading music Soulseek is my main source. I might grab a torrent here and there for a specific release or when it’s just a mess to get with Soulseek (like the Final Fantasy OSTs).
For managing the library and listening to it, Foobar2000 all the way. It can get a while to set it up properly but it will be tailored to your liking. It’s the most advanced player out there. And there are plenty of add-ons (called components) to add features and basically do anything you could need : play MIDI or old consoles music files, play music from Youtube, get tags from Discogs or MusicBrainz, get lyrics, UPnP server… The interface is highly customizable as well. And you can create shortcuts for almost anything, components included (although shortcuts would need a revamp).
Oh and I didn’t told you about queries. That makes tag fields as variables. So now you could make a query on a genre, a codec, an artist… “%codec% IS FLAC” will output only FLAC files. Very, very handy to manage your library. These variables can also be used to rename or move files. You can also use queries to create autoplaylists. These playlists are auto-updated based on the query, you don’t have to maintain them. I have made a bunch for 60s to 2020s music, my favorite artists, or mixed compilations.
A few components to install right away : Playback Statistics and Enhanced Playback Statistics, they will no only give you better play stats (duh) but also new query fields. Masstagger to make batch modification on tags, this will save you a lot of time. Also for now install the 32bits version, many components are not available on the 64bits yet.
So yeah Foobar2000 takes a bit of time, but it’s great, highly customizable. It has saved me dozens if not hundreds of hours to manage my library. And it’s free. It’s my favorite piece or software and I could talk about it all day long.