As most others mentioned there isn't much of a question here but I would like to hopefully be able to point you in the right direction if possible.
First off, the continuous running of the stepper motor, as long as your foot is depressing the pedal, can be done relatively simply. For example, a quick if-statement, could quickly allow you to tell the Arduino, if the switch is closed (foot is pressing the pedal), run the stepper motor at whatever speed you desire. As for controlling with the potentiometer, there are plenty of tutorials online of how to control them with potentiometers, such as this one, https://www.youtube.com/watch?v=RakXequOrSY, which uses a NEMA motor.
Secondly, as for the, "returning to position" qualm, I highly reccomend looking into the accelstepper.h library. There you could potentially use a function such as set
stepper.setCurrentPosition() and put a 0 between the () to tell it to return to the home position once you release your foot (add this into your if-statment if you choose to go that route. This same library could also be quite useful for the initial running of the motor, maybe using a function such as
stepper.runToNewPosition(), among many other possibilities.
Lastly, as for the pushwheels, I do not have much experience using those so maybe someone else could help you on that front. Hope this helped a bit.