It's going to be tough to get the bearing holes aligned based on the tolerances on the sheet-metal bends. This will be even tougher because your design doesn't have a flat surface parallel to the bend line that the brake operator can use as a back-stop.
Correct bevel-gear alignment is VERY important in a design like this, especially if you're using a "small" bevel gear. My advice would be to use the one Aren suggested (good size for this application).
You should consider making your bottom wheel-axle into a structural axle (make it into a standoff with both ends tapped, or (148's favorite trick) make it 1/2" OD tube with a 1/4" ID, then run a 1/4" bolt through it. Making the axle a structural member in this way will GREATLY stiffen up your module. Right now I'd be concerned that the forces on the module will "unbend" the sheetmetal -- you should do something to turn the module into a box structure.
Ohh -- I almost forgot: don't do a swerve drive.
The cost is greater than the benefit in almost ALL situations for almost ALL teams.
-John