Assuming you're making a five gallon batch, 12lbs of Wheat LME + .75lbs of Crystal will yield an OG of 1.074. That's a little high, but it's not outside the range of what I would use the hefe yeast for. I would, however, make a starter instead of just using two vials. I would also step the starter up a couple of times, so that the yeast is as healthy as possible for the larger beer.
The trappist yeast is fine too, but will give you a different flavor.