More Sump Questions... Experts please help!

[brizzo]

-What pump brand/size do you recommend?

I've had success using mag drive and rio pumps for submersible in-sump return pump. I would lean towards a Rio 2100, since it should be around 300gph at 5'. And of course, install a ball valve to control flow.

-How large do you recommend making the return section, (I have a
auto-top-off)?

The bigger the better, per say. When evaporation takes place, the water level in your return chamber is going to lower. Use google to calculate the water volume (ie: "(12 * 12 * 8) cubic inches to gallons" )