Just to add to my last post, you might want to start by registering your site with one of the adult pass networks like Adult Check (
http://www.adultcheck.com). They will probably take care of a lot of things for you, like advertising. This doesn't mean you shouldn't do your homework, but it's probably a good place to start. There will most likely be some sort of contract or agreement, but once your site gets popular enough (if it does), then you can consider going at it alone. At least then you'll know whether there's an audience for your product or not.