i agree with enigma on the chiller, you could eliminate two holes in your sump by going from the sump thru the chiller and back to the tank all in one line. the side the water spills into from the tank (the right side on your diagram) would have a constant depth of 7 inches (the height of the bottom baffle. the autotopoff controller should go in the side with the return to the tank, since that is the level that will decrease with evaporation. it doesnt matter where you drip in the topoff water.