Be careful when cleaning, but it is always a good idea to clean it up before you start. Never spray cold water on the IP when it is hot, there are some delicate machined parts in there. Wait til it is cool before washing that down.
There is a vent on top of the trans, water can get in there also. not smart to rinse in that area. If you spray down the rear of the engine water will run right towards that vent.
I would get a set of allen head 3/8 drive sockets for your Benz, there are lots of those to work on as you go. You will need a couple of sizes to remove the motor mounts. There is one that requires an medium extension to reach. That one is accessed from under the engine cradle. It can be tough to loosen. I had one that I used an electric impact wrench to rattle loose. Be sure to use a little anti seize paste on the threads when reinstalled.
The trans mount is easy, either check a Haynes manual or climb under there and figure it out.
You will need to get the car up so you can work under it, always use quality jack stands to support it, or you could have an adventure you do not want to think about. You will need to raise the motor once you have the two lower bolts out from underneath. Then there are three bolts on the top of the mounts, the engine needs to be raised to get to the inside one.
The shocks usually get in the way and will need to be unbolted to get to the mounts.