Windows 7 Server build

Sure, I'm sure that most of us in the field have had some experience with such cabinets.
I don't suspect that heat would generally be an issue, since in most cases the back of such cabinets are either wire mesh, or wide open and the fronts can be left open or temporarily removed and most have fans to facilitate air flow, but you can always augment them with a couple floor fans if needed.
I would think that perhaps cabling might be a nightmare, since before as I understood it you had more or less a linear bus type setup where you cascaded one switch to the next to the next located on each table terminating with the primary switch now, at least in my imagination, you would have home runs from each client machine to a central cabinet, looking more or less like a spoke and wheel hub type spiderweb involving the use of many more longer cables. And I suppose that noise might be at least a small consideration (the cabinet may sound like a small helicopter getting ready to take off), but if everyone is wearing headsets then maybe not.
The concept is a good one and will almost certainly make moving all the components from site to site much easier, some cabinets even have wheels, which I personally never found very helpful since I never moved them around much after they were set up, but in your case may prove beneficial. I would only suggest that you shop around a bit and make sure that the cabinet is made of strong (heavy gauge) material, so it doesn't bend and flex alot during the moves as this will ultimately end up in cracks and splitting and door hinges that will no longer open and close correctly. I only wish I had the make and model number of one I had a while back that came as part of a Compaq 8u server purchase, it would be almost perfect for your application, plenty of room and lots of fans.