Hey Brendan,
Wrong group to ask if a tank is too big.
Most here would flood there basement and turn it into a snorkaling pool if they could.
Some real Q's though, Were are you going to put it? Inside wall? outside wall?
Do you have an area in mind for the tank, meaure that and see what size tanks will fit.
What kind of tank? Reef? FOWLR?
The more info the better we can help.
Dan