If I assume correctly judging by your registration date you're fairly new at this (no offence) and you are looking for a text book JAA/CAA answer (if not just ignore me).
With reference to Q2 Capt Pitbull is absolutely correct but just to put it in terms of exam questions.
At a constant attitude Lowering the flaps increases the angle of attack of the wing. Extending the slats decreases it.
It might be worth noting that the aerodynamic chord is the straight line between the forward tip of leading edge of the wing and the tip of the rearmost trailing edge. So if you change the position of the leading/trailing edge the chord must change. Sketch it out to see how.
As far as density alt is concerned I have read and been told the best way to calculate it is on the flight computer (crappy-5/E6B) so that's how I do it. It's only a 30 sec job after all.