The M111 DOHC four cylinder engine uses a double row timing chain that should last a minimum of 250,000 kilometers if you change the oil/filter with regularity. No MB engine uses a timing belt.
You won't need to set the idle on that engine. Computers do most of that kinda stuff for us now. Timing, mixture, idle speed, etc. are all a function of your car's brain.
Changing the trans fluid on the 722.6 five-speed auto is a little more complicated than on conventional trannies. You MUST use the MB synthetic fluid, and when you set the level, the fluid must be at 80C. Your tranny has no dipstick, so if your shop does not have one, they'll have to buy one. This is an important task to do properly, as your electronic tranny is sensitive to fluid level.
Replace the brake fluid, as Paul said. Keeping it clean is important for brake compnent life. As to the coolant, use the MB coolant. It is a neutral ph, and breaks down very slowly compared to most coolants. As your cylinder head is aluminum and the rad is plastic, you need the right stuff for longevity.
You should be changing the cabin dust filter and engine air filter more often than 30K-miles. The cabin dust filter not only keeps clean air flowing to the occupants, but to the AC evaporator as well. You will increase the life of your AC components by changing it at least every 10K-miles. I change the engine air filter at the same time, as keeping it clean is rumoured to extend MAS life, as well as keeping crap out of your intake and engine.
If you have been running a high quality premium gasoline in the car, you probably won't need any additives. The detergent agents in premium gas are 99% of the time more than adequate.
1998 C230 "Black Betty"