I agree with getting a good book and reading.......I strongly think your going to have issues with the mixing of the clowns......If the tank was "huge" "huge" you would be able to get away with it possibly, but not in that size of a tank...
I do disagree with the theory of not mixing Tangs of same body style.......I keep an Achilles, Powder Blue, Yellow, Purple, and Blond Male Naso all in the same tank without problems.....I don't even know if the rule of odd numbers really works, because I've tried and suggested that before and they always seem to go at it at the begininng till they figure the pecking order......