[Duckhams]

Im definitely not going to dissuade you from over building it, a strong stand is a good stand, but this is one I built a while back and it was seriously over built. Remember that most commercial stands are only plywood, and they hold up. Some well chosen, straight (as best you can find) 2x4's and you'll be fine. You have a solid start there (no pun intended).
I should note that the final build had a center brace in the back and one in the middle of the top surface. I used a 1/2" plyboard top and bottom which really made it solid, and skinned it with 1/4" ply.