Mike, Here's what I did on mine. You could use the area that I filled with bio media for a moss refuge/filter. I do that on salt tanks with Caulerpa algae. Since the baffle are really only being used to force the water down and back through the next stage of the sump, they can be closer than 2" as mine are (i want to get a hand in to clean if needed). Many reefers are now using 1" baffles in an attempt to control bubbles which aren't nearly the problem for f/w. It's interesting you mentioned the moss grow area as I had considered it, but decided I wanted to keep the sump barebottomed to help control buildup of detritus which seems to collect badly in sumps IME. You will almost always need more pump than you think for the return. Go big and ball valve it down if needed.
You're at the fun part of sump design, getting to make it exactly how you want it., Good luck.