Oh, and on the return pumps, you shouldnt need more than a hammerhead or 'cuda on there... you only need 1.5-2x the main tank volume per hour going through the sump/skimmer. Save the cost, wattage, flow, etc for the flow in the main tank.
Here is a diagram of the tunze boxes I was talking about...
Much easier, safer, and effective than plumbing closed loops. The boxes could even be removable (like large waveboxes), clamped to the side walls or something, because they arent overflows or anything that has to be sealed. One tunze controller can run 8 pumps with two Y-adapters (7092.340).