I would see no problem with adding two small clowns both of the same species. You can also add a clean-up crew, which will also help you get rid of any left over food, if some happens to make it to the bottom. Inverts don't add that much of a load and your tank won't recycle, just remember that you won't be able to add any fish that think of inverts as food, like puffers, triggers.. unless of course you don't care if they are eaten.