with lighting I usually cut holes in the top of the cage put screen on the inside of the whole and mount the lights to the hole. This works if you do not want to stack. If you want to stack build a wood box with the top and bottom open that will hold the light. Mount the box to the inside of the cage and install a screen over the open end of the box.
Dimmer switches are easy. Every 120 volt product ie lights, heat lamp, and heat tape has at least two wires, some have a third green wire for ground, but most do not. Take one of the two wires and cut it. Seperate it from the other wire both toward the plug and away from the plug about 8". Strip off 1/4" off each end of the cut wire.
The dimmer switch will have 3 wires. Usually two black and one green. Don't worry about the green (unless the device you are connecting has a green) if so then you will connect green to green. Connect one of the black wires to one end of the cut wire and connect the other end to the other black wire. You should be up and running. Feel free to email with questions.
tom
xtremeherps@yahoo.com