Hi and Welcome to Just Answer! I am Pavlin, how are you?
I prefer to drain oil using drain plug, why, because siply using gravity, oil and all Engine internal combustion product that we do not want into the engine will be drained. this is what I think, and it does not take much anyway.
best is if you do is with hot Engine, so oil is light and most of it will drain. turn of hot engine and wait 5 minutes, then drain the oil.
Fill capacity fith filter replacement is 7.5L
sorry, I mean with filter
those are the approved MB oils, but Mobill-1 is good oil
as we are in the middle of winter time, I will recommend you go with 0w30 oil or 0w40 as it will have better viscosity when cold.
when draining the oil, let oil drain plug open for few minutes for maximum waste oil drain. replace drain plug coper seal and oil filter rubber rings supplied with new filter. tight drain plug to 30nm or 22 ft lbs and oil filter to 25NM or 18 ft lbs