Looking for calculations

I have been working on a small ev for remote operation, basically it is a two wheel (rear drive, front steer) unit, not much bigger than a mobility scooter.
Here is my question to the gurus here, where do I find the necessary calculations I need to make this thing work as imagined?

Come on people, what do you do in this situation, just go out and buy a motor and hope it works?, and when it doesn’t pull your ride, you say darn! that was the wrong motor?