Let me know what you think of my 54 gallon reef

[andestang]

Emergency over flow is a must, float switches and such for pump shut down are nice, but you would not really need them with a emergency overflow set-up. As for a sump over flow(more likely - power outage etc ) such as for when a pump shuts down and the return line back siphons, a margin of available empty space is required to handle this - here a link for a rough estimate
http://www.reefcentral.com/index.php/sump-volume - you could also add a check valve in the return line to prevent back siphoning or add a bleed hole in the return outlet just below your water line in the tank. Just a few quick idea's.