Paul, I like your simple approach, we tend to overbuild benchwork. 
I had a similar idea, but wasn't sure it would be sturdy enough. The only real difference is 3 cross members and 2 rails would be different lengths to support some overhang. The black dots are leg locations and I might use plywood triangle plates instead of braces. I plan to rip 3/4" plywood into 3" strips for the framing and it will have 3 levels, so I might use L-shaped legs instead of the 2x2s. I plan to cover it with 3 sheets of plywood, but haven;t decided between 1/2" and 3/4", though I think 3/4" would be best because of the smaller upper levels. The risers would be placed on top of the cross members to minimize sagging, so 1/2" might work okay. Decking will be covered with carpet padding or cork and white batting for a winter scene in Bedford Falls from the movie. May I ask why you added the 2x4 cross member to the module?
