really no need for a divider between the "in" drain area and the skimmer, water level will be maintained with the other baffles, and it's nice to have the extra space if you change skimmers down the road. a filter sock on the drain always helps.
if you put the refugium in the sump, make sure you have a valve on the fuge side to drop the flow rate. with this setup I would be partial to running the drain straight down the left side into a sweeping 90 with a T going down to the fuge and continuing across the sump with another sweeping 90 into the "in section". this will keep more water flowing and reduce the noise of the T as you have illustrated above.