Motors/Gearboxes required to move a 20 kg/44 lb robot

[ArchVince]

After the last drive system was too weak to move the robot, it seems prudent to check the current plan before proceeding.

Robot Specs:
This isn't for use in a FIRST event, so the drive system doesn't need to comply to FIRST regulations. The robot is ~20 kg (44 lbs), with a 38 cm x 38 cm (15" x 15") wheelbase. We're looking for top speed of 1.5-2 m/s (5-6.5 ft/s).

Drive System Specs:
Four 5" wheels, of which the two rear wheels are powered by one BaneBot RS775 motor each. The wheels will be attached directly to the output shaft of the gearboxes on the motors, which will be VersaPlanetary 50:1 gearboxes. The current plan is to use the 18V RS775, but to run them at 12V.

Parts:
RS775 Motor
VersaPlanetary Gearbox

If someone could confirm that this will be sufficient power, I'd appreciate it. If any other information is needed, let me know.

Suggestions of other drive systems are also welcomed, as no one working on this specializes in this area. If you do want to suggest something different, here is some potentially helpful information:

Wheel size is limited to between 4"-6" due to the frame construction.
The motors will be on 40 amp fuses (10 amp fuses if we can get away with it, but that seems unlikely).

Side question, as long as I have a thread: If I have the wheels as close to the gears on the output shaft as possible, would I still need to worry about supporting the shaft to protect the planetary gearbox?

Thanks.