the last challenge is: how to detect if a stepper-motor is rotating

[donotdespisethesnake]

we are wasting our time

I have already solved the problem with a HAL sensor, attached to flat-cable. You can avoid wasting your precious time.

Common stepper drivers such as A4988 etc use a PWM output to the motor, I'm interested to see how the Hall sensor copes with that (I assume you mean Hall sensor).