12 inch is a big wheel on a feather - 100mm / 125mm is much more common

You need to gear for around 10 mph top speed. Going much higher then you will likely have control issues

With the motors and wheels you also need to consider the torque you will get out of the motor when combined with the wheel.

In simple terms a cordless drill motor/gearbox and 12 inch wheels will have low torque (pushing power) and too high a top speed