I understand that the clean up crew really doesn't count since they "Earn their keep" but do corals need a certain amount of water per given size? I would assume that I would want to keep them from touching each other but Is there some type of ratio as to how big or how many or what kind of corals to have to how much water in the tank?
Try to go with a site specific theme if possible... Imagine that you will want your corals to be able to reach mature colony sizes in their max(at which time, your main task will be maintainance via propegation and fraggimg). If this help any, the more room and bulk water, the better off you will be.
There's nowhere else I'ld rather be... unless, of course, you're buying
some corals are very aggressive, take a galxea for instance, I have seen mine send out sweepers 6" long and literally melt a small colony of xenia, you will want to give them room to grow (as repto said) and so they are not engaging in "coral warfare"