If you provide your visitors with full galleries then they will not buy anything anymore because they can get it from your site. The same with tubes, if you post full length videos then there is no reason for them to buy anything because they can have it on your tube site.
For this kind of site, you should sign up for some affiliate programs and get their promotional content and populate your porn site with them and post affiliate links in each post so your visitors can join paysites.
I have seen that BangBrosOnline have big ass paysites and NastyDollars (now AdultForce) also have them too.
Besides that, it is not that bad. You should add your main keywords in your post titles so you get some traffic from Google for them.