A truly low mileage MB Diesel is getting hard to find. Most of these cars are coming in with a lot of stuff like you are describing.
Your question is based on the economics, and what may come down the pipe as costs to you. Most of that stuff you list is what we are all working on now, or have been, or probably will be in the future. These cars are getting older.
I don't see that this car will collapse on you, but anything is possible. You paid a premium to get a lower mileage diesel, and the stuff that is bad sounds like it is mostly from age, not the miles.
That paint work would be the only thing that most of us would not tackle. Is it good enough to live with? Before giving up on the car you might check with some local shops to see if it could be polished out to match better, but that is a long shot with most bad paint jobs.