As far as light leaks you can build a duct that "zig zags" and will cut down on the leakage.. possibly eliminate it altogether. But theres still nothing to control odor, which should be your #1 concern in a stealth (or most any) type of setup.. 125ish CFL watts, first time grower... if you pull 2 ozs (total)then you are on the right track.

Just looking at your drawing, I'd put the intakes on the other side of the box and low, with the fan blowing out from the top opposite side. This way it will draw the cooler intake air across the ladies and up and out.. not to mention that heat rises, so the heat from the lights will be exhausted more efficiently as well. Have the 12" fan exhaust and blow into a homemade scrubber using kitty litter pearls (instead of carbon) and it should control the smell fairly well.. the CFM of the fan is very important - what brand/model is the 12" fan?