Thanks for all the comments, we switched to a globe motor on the front with a pot and now have around 55 degrees of steering lock (on the inside wheel, it's ackerman so around 40 deg on the outside) and no issues with power. The wheels won't be exposed, we're going to run bumpers all the way around and nothing is going to be attached to the front or rear end so that they aren't stressed in an accident and are easy to remove for repairs if need be. The robot is pretty much finished now (except for the bumpers), I have a couple of pics of it, see below:
Total weight as shown is 84lbs. We figure we might get it up to 90lbs with bumper mounting brackets and the cage around the front and rear wheels, so still 30lbs under weight.