1) the dash indicator 1-3 is the oil pressure and not the oil level. Thus while you might have enough pressure, you may be losing oil.
2) the yellow dash light warns about the oil level, not that it is time to change your oil.
In light of these two items, you might just want to top off the oil in your sump if your last oil change wasn't too many miles ago. If you do decide to change your oil, 10/30 is a good all around viscosity unless you live in a subfreezing climate. In which case God help you 'cause shoveling snow is a b***h. And be sure that the first number is lower i.e., 5/30 or even 0/30.
Regarding your sump capacity, most MBs are rather large, about 8-9 quarts! If you drain it from the bottom into one of those disposable boxes, be sure to use two, otherwise you'll have an Exxon Valdez on your driveway. A quick call to your local MB dealer will provide the definitive answer. And as always, never fill your sum in one shot. Put in say, the first six quarts and then check your dipstick and add the rest accordingly.
By the way, if your oil light is going on, you are losing/burning oil. You might want to deal with that issue first.