You live in Virginia, and if your state gets over 2" snow in winter you should follow the severe maintenance intervals in your owners book.
The suggestions about the repairs and services are the following.

Brake Pads: Pads should be replaced when the thicknes falls below 30% of a new pad thicknes, you should never wait 'till it is metal to metal since this will produce excessive heat that may damage your caliper seals and other expensive components. It is important to measure all 4 wheels for thickness, keep in mind that mercedes OEM rotor are composite material and cannot should not be machined, replacement is required with installation of new pads and sensors.(sensors should be replaced with the pads).

Coolant Flush: A coolanr flush is recommended every 30K to avoid corrossion of other build up inside the cooling system, this is preventive maintenance and is not required but will save you a lot of bucks on the long run. To perform a "Flush" you need an special(expensive) machine that a blue-lite tech may not have handy, that can be a good reaqson that he is recommending a drain and fill, instead of a flush. A flush will clean the inside of the angine, hea ter core and radiator, a drain and fill onli fills the raddiator and does not wahs and clean any additional components. A cleaning(flush) solutions is required in every flush.

Bushing: Bushingsd sre nade out of rubber and ruber has a short life, usually no longer that 5 years, if stress and dryrotting is becomming aparent , it is a lot cheaper to replace the bushing today and not an expensive contorl are sometime later.