IMHO, take back the clarkii and damsel first off, and then I see no problems with the perc, cardinal, and blenny in a 30 gall. The reason I say this is b/c 2 different clowns in that small of a tank will end up fighting and the damsel is just an SOB, or will be soon. Don't overload the tank, I only have 4 fish (1 to be moved to a larger tank) in a 75 gall. reef (beginners reef) and with a reef it is more about the corals then the fish. HTH