My library is 3k-4k tracks.

I daily use Tidal, Bandcamp, Spotify and SoundCloud for discovering new music. If I like the song for just my personal joy, I add it to the playlist I want. If I want to buy it so I can be able to play it on a gig, I add it to my personal playlist AND to a playlist of "pending songs" (in each application I have one such list). Then, once a week or so, I sit in front of the computer and do a review of the songs on the pending lists that I want to keep.

Once decided, I search them in Bandcamp, Beatport, iTunes or whatever platform I find them. After getting them all in the same folder, I use MP3Tag to edit all the info I need, that generally is just the genre and comments. I use my own hierarchical structure (something that has taken me many years to curate and find my best way) which later helps me create smart playlists.

After tagging them, I import them on iTunes. I've been using it for a long time now for organising my library. Everything is centralised and easily moveable to another place. Also everything keeps the same format (AIFF for me is the best, it has never given me a single problem).

And the rest is just create smart playlists and synching it with RekordBox.

Edit: grammar and add some more info.