You'll need to make the base strong as shit, 5 foot is a pretty good span for plywood on rollers, you may need to put a set of rollers or two in the middle so it doesn't sag and screw up over time. Remember that it is a warm moist enviroment with the wieght of the pots sittin on top, so iot's goin to give a little no matter what.
I would run a 4ft. T5 with 4 bulbs on your veg side, you might even could get away with a two bulb setup.
I would run a 600w in the flower side and an air-cooled hood is probably the best way to go, batwings make it hard to capture the heat from the bulb and get it out of the space. I would run 4 plants in 3 gallon pots or 4 individual Waterfarms.
Air circulation and exhaust are critical so get a 400+cfm fan kickin to pull the heat out. I would get a small circulation fan in the veg, clone, and flower area.
12" for the clone section is goin to be tight, keep in mind the the light you mount in there will eat up a few inches of your verticle hieght as well as your pots, so 12" becomes 6" real quick and your screwed.
Check Woody's thread on the same, he did an excellent job puttin his together, it will answer alot of your questions
Tex