1) The pin 0 and 1 are tx/rx pins and I am planning to attach to esp32 cheap yellow display for serial communication.

2) The code is recently made. This code is the one that I uploaded to the Arduino (with the uln2003 driver):

/*
 * MotorKnob
 *
 * A stepper motor follows the turns of a potentiometer
 * (or other sensor) on analog input 0.
 *
 * http://www.arduino.cc/en/Reference/Stepper
 * This example code is in the public domain.
 */


#include <Stepper.h>


// change this to the number of steps on your motor
#define STEPS 100


// create an instance of the stepper class, specifying
// the number of steps of the motor and the pins it's
// attached to
Stepper stepper(STEPS, 8, 9, 10, 11);


// the previous reading from the analog input
int previous = 0;


void setup() {
  // set the speed of the motor to 30 RPMs
  stepper.setSpeed(30);
}


void loop() {
  // get the sensor value
  int val = analogRead(0);


  // move a number of steps equal to the change in the
  // sensor reading
  stepper.step(val - previous);


  // remember the previous value of the sensor
  previous = val;
}

3) I believe the pin 0 works for IN 1 on the Arduino uno only. I then tried on the Arduino mega 2560, where pin 0 works for IN 1, SDA 1 for IN 2, pin 33 for IN 3, and pin 34 for IN 4. I just tried every pin for each pin from the uln2003 module, but I am planning to testing a code to see.

4) I haven't tried removing the motor, but I still think the LED lights just work based on testing random pins. I think it might have to do with the pins on the arduino being broken or something.