I have almost exactly the same setup you have - 90g AGA and a 30g sump that I'm about to create out of a tank. I thought about using the return line as another drain, but was told on another board that the single drain could support 700-800gph, which I thought would be sufficient...but now I'm second guessing that.
What does the SeaSwirl do? Is that the unit that rotates through 2-8 different returns to create misc currents in the tank?
What type of ps are you going to use?
My sump will be in the basement, but elevated off the floor about 4', but I was going to use something like a Mag 18 (or equivalent) to pump water back up.