Here are answers to your questions (Changing oil on the M119 engine):
1. Oil filter on the M119 engine is located below the flexible air duct. When facing the engine, this air duct is located to the front left of the engine.
2. No special tool needed. You only need a 13mm socket to loosen center screw and remove screw together with oil filter cover.
3. Only one drain plug. I believe it's also 13 mm. Need to remove sound encapsulation to access drain plug.
Other Tips (You may also want to do a search on changing oil):
1. Make sure you change the oil while engine is hot. But be careful, hot oil may scald you.
2. When old oil flow has diminished to an occasional drip, reinstall drain plug with new metal sealing washer and tighten plug to 40 Nm (30ft-lb).
3. Need to change two rubber o-rings in the oil filter cover and housing. Lubricate with new oil and install new O-rings.
4. Install new filter cartridge with large rubber seal on cartridge pointing down.
5. Install oil filter cover and tighten center screw. Tightening torque is 20 Nm (15 ft-lb).
6. Refill crankcase with oil. I think oil capacity is 8 liters (8.45qts.) Pls. check your manual.
7. Allow engine to run for a few minutes to circulate new oil, then check for leaks at drain plug and oil filter. Stop engine, wait 2 minutes, then recheck oil level.
8. Reinstall flexible air duct and sound encapsulation.