Looks like your research has really paid off, looks very clean and well organized. If you add a sponge prefilter or some sort of filter sock/media bag to try to reduce the air bubbles in the output it will need almost daily cleaning to avoid nutrient build ups and creating more nitrates. Not sure if you have room to build and H trap to isolate the air from the over from getting into the sump, it looks pretty tight in there, Great use of available space though.

The dramatic drop in nitrates is likely do to adding 30% more water to the entire system. Overall you should be far better off than the wet/dry filtration could offer.

Can you describe the method of water flow through the sump/fuge? Maybe it's just the angle of the pictures, but I don't see the return line or pump, I would guess water enters on the right as pictured into the skimmer chamber from your overflow, water then spills to pass thru the refgium and is returned through the left most chamber... just don't see a pump there.