They approved your account, so I would contact somebody like an account manager there, AdWords, and talk to them. AdWords is good method of advertising, and it is 10 times better than banner ads, lets say, as people search exactly for what you will be trying to advertise. If you can do it, and then do it correctly, it can be a good and profitable thing. None of the ad networks, that I mentioned will have something as good as AdWords or traffic from search (people search for "sign up to xxx paysite", "buy paysite membership", and this will convert). When people see a banner on a website, is has some effect, but it is like 10 times less effective, than good traffic from search (also AdWords). If you can do it, I would work on that, but you would need to focus, or even get some good people to work on this. You cant work on something else 90% of the time, spend $100 per day on AdWords at the end of the day, see how it goes... This wont work.
I am not sure if there will be info about xxx sites at
semrush.com, but you can check it out. It is probably the best research website, for what you would be trying to do. You could get a lot of keywords and other data, from there. There is other tools too. If you can do it, I would go over some books from
amazon.com
Dating websites are ok for AdWords, and if you would do the research with
semrush.com, it would show you, that close to 50% of dating domains, actively advertise through AdWords.
10 days free trial at SafariBooksOnline.com