[FourPenguins]

If you're looking to build that sort of omni drive, I see no reason your plan (4 tough boxes, 4 CIMs) won't work. Be careful to:
a) Do the math on the speed/torque this combination will yield (searching CD will get you lots of help with this, and many in this thread can assist).
b) Take into account that some of your speed/torque will be lost to wheel scrub (the wheels will be driving against each other as well as forward/backward). I'm sure someone here knows more about this than I do.

I'd say your first step is to define your goals. Speed? Pushing power? Terrain ability? (this type of DT works best only on flat ground)
From there, work back to your desired gear ratio. See if the toughboxes are within your needs. If they aren't, you can modify them pretty easily by swapping out a stage or two, or adding a stage after the gearbox. You could also design and manufacture your own boxes, but I gather you don't have the resources for this.