If that lens is fast enough for your application, I've got a Tokina 80-400 which actually is made out of metal (although the hood is plastic just like the Nikon). I didn't mention it above because I figured that it wouldn't be the best choice for what you're doing - but it is quite a bit less expensive than a 2.8 zoom. It's very sharp until you get over 300, then it's a little soft - but 400mm is probably not useful to you anyway. Two large prints made with this lens in the 200mm range confirm this! I have the latest version which I guess is a big improvement over the first version. The current one has a tripod mount on the lens, and it's got a "II" in the part number. The minimum focusing distance (if I remember right) is about 6' or 7' though - if that doesn't work for you, you could add an extension ring to shorten that distance.

Your other question - yes, you can add halogen lamps to increase brightness. That's one great thing about digital, you can adjust the white balance so that halogen light appears white in the finished image instead of yellow which is how it would normally (i.e. daylight film) be rendered. There would be some issues with heat with these too - but probably more for the internal wiring of the fixture than anything else.