Here is a link showing photos of using raceways - http://www.cnidarianreef.com/mequip.cfm
Personally I would skip the power compacts and use T5HO's. The T5's are much more energy efficient and a lot brighter. What do you plan on using the T5's for, actinic supplementation?
I would not glue the acrylic to the plywood. It will be plenty strong enough just resting on the plywood. I have seen a frag tank 8'x4'x16" made out of nothing but 1/4" acrylic but personally I would have opted for 3/8" just to be safe.
A float switch can be used in creating an auto-top off system but I'm not sure how it would regulate the flow in the sump. When you mentioned that you read where someone was having problems with the flow rate in the sump was it because the sump held too small of a volume of water or that the return pump was able to pump water back into the tank faster than the overflows could return it to the sump? Using a 55 gallon sump and rating your overflow to at least 1.5 time the output of your pump should solve these problems. Do you have a link to what you were reading before? Maybe I am missing something.
A float switch and a checkvalve should not be needed on the return pump.