Congratulations Manu!

I'll take the first stab at it but I'm sure the other 500E brothers will chime in and help you out.

My sunroof doesn't rattle but I do know that when I close my doors...when the door "thuds", the sunroof really jumps in its place. I think this is indicative of all sunroofs as it is not an integral part of the roof. Maybe the rubber weatherseal has gone too flat and not cushioning anymore?

Do a search on this forum and you will find several threads about 500E sound systems. Michael has a very nice setup.

I wouldn't bother with the rear headsets.

The snowchain button will give the tires more slip tolerance before the ASR is activated. But this is only under a certain speed. Basically not an ASR Defeat switch for us speed (fun) hungry drivers.

Good luck and happy driving!