There are two 8"x8" Doran darkroom louvers on the back at the bottom, for intake. You can get those from bhphotovideo.com, about $30 apiece. Completely lightproof. Air comes in through those, then through the carbon filter, past the light, through the fan, and out the top: intake -> carbon filter -> light -> fan -> exhaust. There's also a little desk fan in the back right corner (can't see in the pic) to just move air around some and make the plants happier.
I mostly start with clones. But currently, the back three plants are three female Nirvana Papaya plants grown from seed. (Clones gotta start from somewhere!) The front three are Hindu Kush clones.
I probably could move the scrog screen up or down, but it's actually easier to just move the pots up or down by putting something under them, if I want them closer to the screen. But mainly, I just leave the screen there and let them fill it just as it is.
600w is just perfect for that area: 4' wide x 3' deep is 12 square feet, so exactly 50 watts per square foot. It is *plenty* of light, and more wouldn't make the buds any denser, but I think less would also have a negative effect on yield. I basically built the box around the assumption that there would be a 600 watt light inside, so it's like optimized for the light. In fact, I had the light and reflector and fan and stuff before I even began building the cabinet.
No smell issues at all. And it's not *exactly* a cooltube that I use; it's an air-cooled reflector, same principle, but a bit bigger and with a larger reflector. The bottom of the reflector is tempered glass to help contain the bulb heat (and ensure all the air is cleaned through the filter first before being exhausted). And I've never tried my cabinets with anything but an air-cooled reflector, so I don't really know for sure what the temp difference would be with a parabolic or batwing or something in there...but I imagine that it'd be much hotter than it is with this air-cooled reflector.
Hope that helps!