I agree, you should have a dedicated server to start with. How can you think of operating a paysite if you can't afford your own server? Luke brings up another good point, keeping your affiliate program and your FHGs on different servers.

I have ARS itself on many different servers, and at least four servers handle the FHG bandwidth. Paysites are your money maker, and you don't want them to be brought down by anything, so definitely keep them on their own servers.