You should install DCS World and the install the A-10C from there, there's module manager to handle it. It then asks your serial when installing.
You don't need HOTAS software to use it necessarily. But if you want to, install whenever you want, that's not directly related to game (I assume you mean Target software). If HOTAS needs some core drivers, (I didn't need to install any with Win 7) they can be installed whenever too, game doesn't care.