First stop is the PRS for music website. All your questions are covered there, and there are many ways to make sure you are doing it correctly. My own download site, which makes a bib or two from specially composed music for specific purposes takes a fair amount of time to administer - and in my case, copyright belongs to me, but registering the music with PRS and PPL, so any additional plays get some income is a b it long winded - getting the codes, numbers and other stuff to embed in the music.
If you are going to allow downloading or streaming, you might get a shock when you discover how much clearance of other people's music actually costs. Even hosting can be tricky because the hosting companies can be very wary of music downloads, so may want assurances you have dealt with rights.