A) The bar is 90cm high from the desk top, so the top screen centre can be placed at maybe 2 centimetres less height because of the bracket.
B) The bracket on the pole is a clamp fixed with an Allen screw. Although the necessary Allen key is kept in a holder on the stand itself, I would say that it is neither quick nor practical to adjust the height regularly because you can't really reach it from the front.
C) Yes. My second 27" screen on the stand is relatively high up and clearly tilted forward, the whole thing doesn't wobble a bit when I shake it and doesn't show any other tendency to want to tilt.