It sounds like you dont know what you want. Tell us the base sort of thing we will be dealing with. I say keep it simple. maybe one of those pop behinds, or user placeable, or maybe a banner at the bottom. I think a topsites, and a banner exchange among member's sites would be cool; but only if it isnt too much work. maybe even the sites that make you the most money. FTP is a must. CGI would be good. I,personally, dont care about PHP or MYSQL. Pay for removing banners would be good, but only if its worth it. Its hard to quote a good price because i dont know what you will be offering.
Make your own decisions about bandwidth and space. Maybe have a starting point and increase it if it looks like you will be able to handle it.
maybe you should go for unlimited bandwidth and space