Debounce is not needed: upon press the sequence starts, but until it's done any subsequent presses on the same button don't do anything.
What is needed is pin labels indeed. No idea what it's doing.
Also details on the driver and motor used. Your code appears to put the stepper through 500 steps (in many steppers that would be 2 1/2 rotation) in 1 second, which may be too fast for the motor, depending on the motor and the load it has to move.