500kb has nothing to do with copyright. If you post 2b of a sound track, its still copyrighted.
500kb has to do with the fact that no one wants to spend 4 days downloading 6gb worth of music to get on your server.
No. The whole song is copyrighted. If you use bits & pieces, it's not copyrighted. If you use the full song, you must change 7 notes and 7 words. What I would do is distort them and be free from lawsuits.