If you can stack the tanks, one over the other, you can use the waterfall method, pump water from the sump up to the top tank, have the overflow from that tank go into the tank below it and then from the lower level tank into the wet/dry. You can run twice as many tanks on half the pumps as long as the wet/dry is large enough for the tanks it is set up to support. Sponges are great, but my fish (the larger ones) have a habit of eating them. In a breeder tank or a fry grow out tank they cant be beat, for a housing tank / display tank, I stay off the sponges.
Sponge Seed tip
.To seed sponges, throw a few in the sump to your wet/dry and leave them there for a few weeks. I keep a few in my sumps at all times as back up, on hand ready Bio Filters in case I need to separate a fish or get some new fish I need to set a tank up for.