That's way too many fish for a 75. I'd cut the tang--they really need a 6 foot tank to be happy, and the chromis. The chromis do school in the wild, but in aquariums, tend to beat the heck out of each other pretty quickly. The percula, angel, and gramma will be okay. The dragonette is a tricky one. The juveniles rarely take to prepared foods, and with a 75 gallon tank, you're going to need lots of copopods to keep one healthy. I wouldn't try it in a tank less than 1 year stable (not one year old--one year without any problems, diseases, or competitors for the pods).
For order--the gramma should be first. Then the angel, then the clowns. Otherwise, the clowns will claim the entire tank, and will beat up any new fish. You'll end up with a gramma that hides constantly, and an angel that may not eat--not an ideal situation.
However--you refer to the clowns as being hardy. While they are, this is not really any reason to add them first. The tank should be cycled before any fish are added. Get the live rock before adding any fish, as this will help stabilize the tank, and provide shelter for the fish--reducing their stress.
HTH