Sump Design

[mark]

Looks good, a few comments:

-with planning, your safety overflow isn't required, you'll only be playing with so much water. If you are going to have one, place right at the top so it doesn't drain every time you shut your return pump off
-consider removing the baffle between the return and skimmer. You can build a bubble tower in the corner just around the return pipe and move skimmer to the front. Use the gain in space for the ref area.
-your pump return is about 7 gallons and depending on your setup could be sucking air after a few days. First I would plan for a auto-top off or second increasing the volume. Could also raise the baffles but would have to allow for water returned to sump with power loss.

No experience but looked into benthic zones also. Here's a link to videos, Sump Concept (right now top, second in) has a sump similar to what your planning. Any reason why the DSB can't be wall to wall between the skimmer on return pump areas and eggcrating covering the whole area?