Connect the pot to the microcontroller as a variable resistive divider. YOu can then measure the voltage to get motor position. From there you code your processor to send out PWM to the motor depending on current motor position and desired position.
Now about how to actually drive the motor by sending it PWM....Do you need continuous rotation or "elbow rotation"? Do you need to be able to reverse directions? If it's a servo motor you need elbow and to be able to reverse direciton. In which case, you need 4 transistors instead of just one:
CHeck out all 3 sections of this:
https://www.modularcircuits.com/h-bridge_secrets1.htm
You also probably need a gate driver that accepts the PWM from the microcontroller and then outputs it to the gate with increased current capacity (and possibly higher voltage) to drive the gate of the MOSFET on and off fast enough. National has a bunch of simple ones. FOr your scale project you should use PMOS transistors for the high-side rather than NMOS (greatly complicates things if you do use NMOS though you get slightly increased performance). Read the link to find out more.