Regarding your last question Miles, yes too much oil is damaging to your engine also. Overfilling for one will eventually damage your catalytic coverter, and the increased oil quanity can cause foaming in the crankcase which is not a good thing. They put the level marks there for a reason - I'm surprised the shop overfilled!
Depending on what wieght of oil was used previously, you could be hearing valve noise on cold startup while the thicker oil takes marginally longer to work it's way into all the passages...
About you first question: I have
heard that valves, and such relating to climate control can be very expensive because of the labor invloved in taking the entire dash apart - that may indeed be what you're in for if you want that fixed
Good luck on your other inquiries!