You've had a lot of good advice here, mach...any other forum WOULD be busting your balls but not in a joking way. We keep it light here. Everyone has good intentions (for the most part :mrgreen: )
In any case, the problem w/ tall tanks is getting the most use of the space. I had a 45g tall tank. I had around 50-60lbs of live rock, and yet it just never seemed full cuz it was hard to stack them up too high w/o risking it collapsing (unless you permanently stick them together).
That said, in freshwater, they tend to follow a surface area guideline in populating a tank, but it's still just a guideline. It would apply to your tall tank...just cuz it's a 56g doesn't mean it will good for a fish that requires 55g...because the fish is looking for swimming area, not water volume, if that makes sense.
You're limited to just the smaller fish. I upgraded to a 125g specifically because I wanted larger fish. But I definitely did not buy the fish until after I got the 125g setup. You never know what will derail your plans.
Be a good sport...take a jab back :)