You put a lot of thought in your system. But... From an experienced cab guy.
Your cab is small. I find it difficult and time intensive to keep a plant tame in a 4' cab. I find it takes more effort to tame the height of the plant than I want to invest in it. At least you had the foresight to realise that the light will take away some of that headroom. Height is a real problem in a cab.
I don't do hydro. I truly respect the dudes that do it and I get why. The benefits are great. It's just that I don't want to commit to adjusting ph everyday. Plus, cabs heat up. Even though I am sure your light doesn't put off the kind of heat HPS or CFL does it will still generate some heat. The enclosed space will heat up fast. Keeping heat issues in check can be done it's just difficult and requires effort. I am not sure how you can keep reservoir temps in check. Unless the ambient temp around the cab is very low. Anyway, I think hydro should be optional. I would prefer soil or hempy bucket in there. Otherwise I do like your hydro unit. Just not my thing.
The light. Yes I agree. You need to encase that thing. Plus, I find that in short confined cabs, side lighting is the best way to go. A light on each side would be a better choice. In my opinion.
Otherwise man I like it. Encase that light and let people do soil in that thing to avoid root rot issues. I think this is an early design and you should make a few changes here and there.
Edit. Screw in some hanging hooks in the corners and at the top to run your wiring out of the way. Keep it off the floor and organize. Also the cab I built had like a 4-5 inch space in the top to put stuff, like the fan filter, power strip, ballast, excess wiring, timer, whatever. You could possibly put your heat sink, power supply and drivers up in their and just hang the cob on its on heat sink/fan. Encased of course. You have a good idea. Just needs a little refining.