Like said before, you should be fine with power compacts(considering only the corals you mentioned before). My personal opinion on the watts per gallon, its just a very general and vague rule of thumb. The reason i say this is because, if you put a coral way up on top, its gonna recieve more light than the corals under your liverock in a cave. If you do achieve 6.5 watts per gallon, dont expect to put a light needing coral in a cave just cause you got 6.5 watts per gallon. The reason we use watts per gallon is just to have a quick reference on how strong the light system really is. But lighting is one of the essential need for good reef keeping. I would say the other things you really, REALLY need is a good skimmer, good water flow, and i almost forgot, A GOOD SKIMMER!