Is it allowed to have a shop in the market where you sell items for USD?

Well i have seen one before so i think it is allowed caprra or something did something like that too i believe but he sold items foor tc too though

Yeah, that's fine. Don't know how much business you'll get though, unless you're selling high value items. Even then it'll be slow. I would recommend selling the items for TC, then selling the TC for USD.