The details are very long and complicated. The simplest way I can answer those 4 questions is: That's the way gravity works.
If you take Newton's law of gravity and his three laws of motion, and massage them properly using some geometry and some calculus, you can show that planets MUST move like Kepler's laws say they do, and like what we see them actually doing in the sky.
(I used to be able to do this, but it's been a while.)
