If you become an affiliate of iTunes all the licensing is taken care of. You are effectively just like a record store, only iTunes will pay the artist/publisher/record company their share out of the sale.
I don't think it's a good idea. Who wants to BUY MP3s when there are tons of them for free out there? I know, they're illegal but as for legal ones we have Itunes which is the best source for all MP3s.