So I want to make a showcase thread to show all of the art I own, but I don't know what sub-forum that would belong to..? I know BenDover made a showcase thread, but I don't think I should post it there.. Anyways, any suggestions or answers would be helpful

Your clan board.

The art board is to display art you've made, and the market art/textures is for selling art you own. Other than that, most boards don't even come close to the thing you want to make.

I don't have access to prime and VIP board, looking at your post background I guess you have. They might accept it there.