you will need high torque motors, better off using a chain or direct drive to the wheels. I recomend using a chain drive if you need it, a chain drive will be better suited due to the lower speeds, and it will be more reliable than belt.

I would recomend motors that have about 15000RPM and alot of torque down low. you might want 12v motors because you could just get a 12v battery or twin 7.2volt packs depending on how big you want to make this thing?