depending on what manufacturers tires you have they will recommend a mileage frame for rotating, having said that five or six thousand miles is a good time frame for rotating. And Mercedes seems to let the rotation be done at each FSS service.
Tire wear will depend on driving style and with your mileage a degree of suspension wear will effect tire wear.
You realize the front and rear tires have different psi settings and for high speed those numbers get bumped up.

As I recall I think my rears get a bit of ouside edge wear at a quicker rate than my fronts.

Flex plates are rubber disc in-line with the drive shaft, they are checked with a flashlight for cracks and distortion.

Ball joints are checked with the car in the air, Mercedes wants virtually no play when rocking back and forth, I don't remember if the movement is vertical or horizontal, and lots of techs allow a bit of play. maybe a quarter inch - but that is a guess.

Squeak on bumps, unless you get under car and play it would be just a guess. With your mieage you can only guess- but they are a know area to have checked. Have you tried just driving one side of the car over a speed bump to see if noise is side dependent?

Change out all the plugs at the same time. Do a search on this forum concerning the inexpensive connectors that can be replaced.

How well does your car idle? how is fuel mileage? acceleration smooth?