2002 BMW 325 Multiple Issues

I have the above vehicle, bought used about 8K ago. Haven't had a single issue noticed when driving. However, had the "Service Engine Soon" light come on and had my passenger window broken resulting in an Airbag light. So, I brought it to a BMW dealer (knowing I'd get gouged) to have them repair these minor issues. The result was the following recommendations from them. My question is general being (for some of the issues) do they truly need repairing, if so how much SHOULD it cost and are these issues indicative of a bigger problem. Car was one owner with good service history. I am also about 5K from needing the second major service on the vehicle.
1 - $250 for airbag plastic seal to prevent water intrusion
2 - $545 for replacement of thermostat (caused Engine Light and for some issues with heating car)
3 - $250 dry and cracked engine belts.
4 - $575 to replace front lower control arms
5 - $690 replace rear brakes (1mm)
6 - $700 recommend consider replacing front brakes (4mm)
7 - replace rear suspension coil springs, one shows crack at base.

From start to finish I felt I was getting screwed at the dealership. I am not super car savvy, but I am no slouch. Some things obviously need repairing but the costs seem ridiculous. Mostly, when I inquired into the details on the issue the worker seemed annoyed and impatient. As if me dropping $4000 when I expected just a few hundred bucks was no big deal.

To whoever takes the time to reply. Thank you kindly!