Nice setup, but I agree that you need a lot more rock. For now it will be fine, with just one fish in. I would highly recommend adding the rock first, as it will be much less stress on you and your fish both. As for the yellow tang, you may end up having a problem with it being extremely aggressive to other fish. Yellow tangs are naturally aggressive, but it is even greater that he is the first and only fish in the tank, he may attack any addition to the tank, as he will feel that it is intruding on his territory.