do you have an mb owners manual for your car-your hood question may be covered in it.

the plugs are indeed under the cover.
this car has direct ignition-there is one coil per cylinder.
your car's tool kit should have a spark plug spanner.

the oil filter is of the paper cartridge type,you have to undo the cover-mercedes benz or fastlane sell a special tool that fits on the cover.also if you look under the diy section of this website under oil filter replacement you will be able to see the oil filter cover location,filter tool and paper cartridge filter in colour pictures.