To the best of my knowledge, a MB warranty is NOT invalidated by a DIY oilchange. But it might be smart to check that out yourself first.
Regarding your choice of oil, the MOST important thing here is that you see MB Spec 229.5
on the can. The weight is something else, and depends on location/climate.
Get yourself a special tool designed for removing the MB filter. Available in many auto stores. Don't use anything else you might have hanging around. There will be a drain plug in the sump, although many folks here swear by the suction method often used by the workshops. A torque wrench is also advisable.
Personally I prefer to drain, as it gives me an opportunity to have a look around underneath the car. Use a new washer on drain plug.
The plastic engine covers on MBs pop up vertically, but mind your knuckles as release can be sudden. It will sit on 4 little mushroom shaped things that fit into clips on the cover. It should not have to come off to get at the dipstick. Put your hood into the vertical position, as it helps access.
Ref your reset facility, what button do you press to reset your trip mileage on the instrument panel? Service reset will likely use the same one.
There are several DIY oil changes covered in the archives here, and also in the 'stickies' at the head of many of the forums. Here's one from the W209 forum for the M112 engine used in some CLKs. Yours will be similar