i'm not familiar with any groupers, but a quick liveaquaria look at their species there are none that will be able to thrive in anything less than 70G.
the tang is also an unfortunately too large fish for a tank your size, they usually require a tank 6' in length for swimming room, when in small tanks they get stressed and are prone to marine ich.
the clown is good, look here(Saltwater Fish: Marine Aquarium Fish for Saltwater Aquariums
) for fish but remember to look at what type of water conditions they live in and their minimum tank size, max length etc.
some smaller wrasses, blennies, plenty of gobies etc. are good choices, just do your research and add fish slowly. have fun!