Perhaps the goal of the project is to combine learning about both steppers and microprocessors at the same time. I agree that a floor sensor system is required , but you only need one sensor and a ribbon with flags to detect relative position. Acceleration would be automatic with the start sequence and deceleration would commence a set pulse count away from the stop position. This presumes that the stepper has been selected to operate properly within its operating curve thus reducing the probability of missed steps to insignificance. Proper design will recognise that the elevator has gotten out of tolerance and run the car to the home position. It would either await a new input or move from home to the correct floor (design specification driven)I will leave the programing tips to the experts but this seems like an awfully good starter project have fun Terry