Total Battery Capacity Necessary for a Middleweight with...

What's the typical battery capacity for a 120 lb bot using 2 S28-150 magmotors and 1 S28-400 magmotor?

And using TWM3M gearboxes for drive and a 45 lb drum if that helps. I know how to roughly calculate the capacity needed given the amps drawn by the motors but the only spec given on RBM for the motors is the max current drawn, and I don't know what percentage of that will be drawn before reaching stall torque and I don't trust my estimations...anyway, would 23 Ah be enough at 26V for 3 min?

That's plenty. You'd probably even be good with 15-ish Ah.

What gauge wiring is normally used for a middleweight?

and would a 13 Ah 29.6 V battery be enough for those motors?