Determining required torque for DC motor

How to determine the required torque while choosing a DC motor?

Here is a simple scenario. Think of a 4WD or 2WD vehicle. The max load the vehicle will have is 100kg.
Q1. How do I determine the required torque for the motor?
Q2. Should the Rated Torque(Kg-cm) more than 100 or the Stall Torque more than 100
Q3. And if use 2 Motor rated at 50kg-cm torque can it carry a load of 100kg?