Oil changes are easy, take a look here:
SLK V6 oil change
This is for the 320, but the process is very similar (see the bottom most photo.). You can drain from the drain plug underneath, but if plan on doing this all the time, you will want to consider an oil sucker of some sort.
The plug is on the oil sump, and you have to remove the lower engine cover, (four screws).
Seals and gaskets come with a Mercedes filter, no worries there.
A special filter tool is very handy, but it can be removed with a strap wrench if you are CAREFUL.
Don't know what the torque numbers are, I always just make them tight, but I have been doing that for over 40 years, so be careful
, the pan is only aluminum and will strip easily. (This is also why it's easier to suck the oil out from the top.)
The filter has an O-ring so bottomed out, and snug is tight enough.