I'm new here. But check out the tutorial section on torque calculations.
It is very good.
I guesstimate the motors will need 14 amps at 12 volts or more.
I posted some questions which led me to windshield wiper motors,
electric scooter motors and bike motors and chain drives.
24 volt, 150 to 800 watt bike motors are a possibility, too.
surpluscenter.com had the best sprocket and chain prices.
Some electric bike and scooter stores were good for parts selection too.
I bought my H-bridge (14 amp, two motor, $65) for bigger amperage after building a
2 amp one for stepper motors. That wiper motor link,
which I posted, had some cheaper regulators. I'm not sure if they
did two direction and PWM speed control. I doubt it.
I think you can do a lot with sprockets and chains at slow speeds on weak motors.
It is interesting to ponder the acceleration and torque required to
raise a 180 lb. man from 40 degrees falling position to upright using a home made segway.
I wonder if any scooter or bike could be modified into a uni-cycle
and then put two in parallel for a segway imitation.
I can see this project getting expensive, even from scratch.