Haha, when I first saw your cab I thought, "Wait...someone jacked my box!" looks almost exactly like the one I just finished building/using
Mine was about the same dimensions (I had an internal area of 24"x24"x48" and out of plywood too!), and here's what I can def say helps:
-Paint that shit! Flat white. Cheap, no extra radiating heat or taped up/dangling bits.
-Get more lights/hang them! Mine was really cheap/ghetto...I drilled four holes up through the top, wide enough just for some hanging wire, ran a screw about an inch or so to the side of the wire, and wrapped the wire around the screws
It was cheap, simple, effective, and I could raise/lower my lights. I had a sorta square bracket setup with reflectors and 6 43w lights going on the bracket.
-Modularize! Get all the power/wires running up top (liquid spills, etc), bring in air from the bottom (I used over sized HEPA filters over my intakes...helps cut down on air restriction which is important in this kinda cab), vent air out towards the top. I also had a sort of tray or rack if you will, that was raised and had all the plants sitting on it in their pots...kept my nutes, tools, etc under there, also helped with light trapping the intakes
-Get more plants in there, and get a fan blowing gently on them. 6 bucks at walmart
Since it's made of wood it's going to reverberate noise which means sticking fans in there is going to make it loud but it's needed as the wood also helps insulate the heat....
To fix the light leaking issue, I had some household door insulation strips on mine and three locks going down the side to keep the door shut completely (with that tall of a wood door it's hard to keep it from not arching eh?). Walmart also has some Duckweather strips or whatever. They're black and look like a V.
I'd take a picture or two of mine but it's currently in a different county oddly enough...
Oh, and keep a fire extinguisher near by...for reals. It's wood. With heat building inside from an electrical light...play it safe and not sorry!