Just curious, but what is the point of having such large returns? There is no good reason to flow thousands of gallons through your sump. If you need extra flow, the best way is to use maxi-mods, Tunzes, or other PHs. The amount of watts the large return pumps use are rediculous as well. You will save alot of power and your fuge (if you have one) will work much more effectively. The other problem that often occurs when flowing too much flow through the sump is microbubbles. The higher the flow, the more there are and the harder it is to keep them out of the display.
I honstely do not think you need more than 1k gph through the sump, and you dont need even close to 2x2" drains to do that.
As for a skimmer, I would get an octopus skimmer rated for atleast 250g+ and do the mesh mod on the impeller (will increase its performance by about 30-40%). For a return pump I would get an external pressure rated panworld rated for ~800gph. They use less wats than a magdrive and put much less heat in the water, plus they are wisper quiet. For extra flow in the tank ,use the obove mentioned power heads.