Read from the potentiometer using analogRead() which should give a value from 0 - 1023.
Use the size of that value to set the duration between stepper motor steps.
Get the stepper motor working as you want before you introduce the complication of the LCD display.
Stepper motors are very power-hungry. If the one you have has sufficient internal resistance when unpowered to hold the camera in position then you can get the Arduino to switch off power while the camera is stationary. Be aware, though, that if someone accidentally moves the camera the Arduino won't know and you will have to move the camera back to the home position to re-establish the step positioning.
You might be able to use a servo to apply a brake to the stepper motor before you switch off the motor power.
...R