As for how much you can make, it depends on how you market it.
The way to make money of TGPs, if you take 100% submitted galleries. Is to sell advertisements. And how much you make off that, depends on how many ads you sell
You can also add hardlinks and your own banners on the TGP and send traffic to your own sponsor, but you cant figure out how much you will make unless you know how much you send. There is no ballpark #