to reset the light, get in the car and make sure the dooe is closed. turn the key on(engine off) hit the r button on the cluster twice to bring up the remaining miles. hold the button down, turn the key fully off, but dont remove the key, and then turn the key back on while continuing to hold the r button. after 10 seconds or so 10000 will show and you are done.
Mercedes rotors do not always need to be replaced, the average is every second set of pads. the only way it wuld be every time is if the car is driven very hard. The fluid should be changed once every 2 years, and also keep in mind the rotors on a mercedes can not be machined due to close tolerances in thickness