I wouldn't keep 2 tangs (maybe a very small hippo, let him adapt as he grows )in a 75; but your list, IMO, is not too heavy. Most of the fish are fairly small and don't add a huge chunk to the bio-load. I ignore the inch rule; 6" of firefish is hardly the bio-load as 6" of puffer. Just don't go too fast, get to know your tank and how it handles increased capacity; the older the tank (as a rule) the more it can handle. Its your tank and, outside of a pending tang war, I see no big problem with your list. I guarantee others will; and I respect their views as well.