This one is a deep question, and you can lose your shirt. There IS a whole lot of money in the adult market. ....that's why everyone and his brother has tried to get in on it. First you need to decide which way you are going to go. Do you want to run this site with your own content (covering eyes now), or other content you put up but is semi-exclusive to your site? Or, do you want to not have yours as the destination but something they browse before clicking on a sponsor that pays you a commission (these are the free ones you referred to)? With these questions comes another....do you want to have people subscribe to your site, or just push them to someone else that pays you a cut and you don't have to worry about the billing? ....what market do you want? What niche/fetish/taste (or lack thereof)?
With these answers, you will know where your traffic will come from.
Good luck, and be careful....there's lots of money, but you have to live it and do it right as there is a lot of competition.