you also have to take into consideration people pushing down on or possibly leaning on the control panel. Is your monitor going to angled? If so, that would help a little with the balance. If it's flat, remember that most of the weight is in the front. I'm not a structural engineer by any means, but it does seem like your cab will be awfully skinny for its height...it's going to stand about 6 feet tall, but the depth is only going to be 22"?
If you can't possibly make it shorter (and use stools instead of standing) or increase the depth, you could put sandbags in the bottom to keep it steady...you definitely don't want the thing to be topheavy.