Looking good!
Couple of things you might want to consider. I know you got the 3 bright lights, but painting the inside of the airbooth white will brighten it up considerably. I made mine out of plain MDF, and while the lighting I had was sufficient, it still looked dark because of the plain nature of the MDF. I just took and old can of flat white spray paint and sprayed the inside surfaces, and it brightened up considerably.
Something else you may consider, because your lights are halogen, once you are finished building it, take a thermometer and stick it in the booth with the lights on. Take a sheet of plastic, or something to cover the opening and see what kind of temps you are getting inside with the lights. You could end up with a makeshift drying booth, which will speed up your cure times. Not such a big deal with acrylics, but if you ever use enamels it could cut your cure time substantually. You could then design a couple of Plexiglas doors (or wood, just thought plexi would be good as you can see through it) for the front of the box that you could close. This would keep dust off of your kits while the paint drys, and create a drying box out of the spray booth. Of course if the temps are too high inside with a cover on it, you could melt plastic....but I think your lights are far enough from the surface you won't have to worry about it.
BTW, your extension cord, White is hot or positive, black is usually your negative, and in this case the green would be ground, however the green and black may be reversed as I have seen some that the black is the ground. However with AC, it doesn't really matter as long as you keep it the same throughout.
Your plug receptacle....that is actually standard now, no center screw for the face plate, screws have been relocated to the outside. Considered the "new" standard apparently.
I don't recall what I used for wire in mine...not quite that heavy, but heavy enough for 110V to the fan. I also soldered and shrink tubed mine. I pulled a plug from an old computer and mounted it to the back, so I could just use a computer power cable to plug it in, ran it through a switch on the front. If I had to do mine again, I would integrate lights into it....I may do it eventually, as I can just pop the top of the booth off and mount lights in it. I do like the idea of pegboard on the back wall of the booth though, too late to add that to mine with out changing alot of things like being able to access the filter and the fan...could mount a small one on the top half I suppose.