Do you have a sump as well? Will the pump be used to circulate water from the sump to the display and to the fuge and to reactors or media chambers, chillers? The amount of plumbing running both vertical (from the pump to the display) and horizontal, the # of ball valves, unions, check valves (hope none), wyes, 90's, 45's all need to be taken into consideration as backpressure when properly sizing a pump.
As you can see, it is not nearly as simple as, 'I have a 24g nano. I built a refugium for it. What size pump would be good for this?'. Sorry to throw the proverbial monkey wrench into the equation. I prefer to do things right the first time