I'm sure he would put opening knobs on the sides. My center area is a key lock, but you don't need it, it's just an option.

I would not place anything on top to the cage unless it is another same sized Pro-line cage. That goes for Boaphile or AP. The cages can take evenly distributed weight and are made for stacking the same sized cages, but in order to put something like your tank on top I'd get a 3/4 in sheet of plywood that is maybe a 1/4 in longer and deeper than the bottom cage and put it on top, and then put the tank on that.

Ed can help you out with ideas regarding his caging.

You'll want a good base for the cage to sit on as well. Something that is at least 1/2 longer than the cage, and 1/2 deeper. It helps the cage maintain it's integrity and prevent sagging and/or improper alignment of the door. Plastic cages are tough, but they are plastic and gravity and weight in the wrong areas can cause minor issues. A few simple precautions will obviously prevent the possible issues I've mentioned.

I hope I answered a few more of your questions.