Sounds like a great adventure! We did a Europe trip a few years back in the 350 and it was a great fun!!
Take lots of pictures, then when you think you have enough, take more
Just taking a few of the items in your list :
Bodywork touch ups - I would maybe wait until you get back, putting a few thousand miles on the car you will no doubt get more chips and marks?
Aircon service - YES!
Aluminium undertray - good idea
New springs all round - Agree with you keeping stock ride height, just incase the roads get unpredictable