I have a similar setup where I have a 300 gallon "mother tank" and 2 x 50 gallon Rubbermaids as a prop tanks. I too have a refugium over the mother, I actually use it more as a skimmer box, but it does have a small refugium section. I actually run my entire 400 gallon system with one Iwaki 100 pump and a 1 Iwaki closed loop that also feeds my chiller. The water is pumped out of my bottom prop tank and the return pump is what drives the skimmer. From there all the water just trickles down each chamber. I have implemented a surge system in my prop tanks that uses zero pumps, nothing but relentless gravity and a few well placed pipes to create a siphon.
I strongly agree with Steven Pro and his suggestions, especially about having two drains. Its always good to have a backup. UV might be a good idea. I would only add that you may want to consider a strict regimen of carbon, and change it frequently. Hope this helps
Cisco
http://www.CulturedMarine.com