I'm an oil change maniac, and the necessity for frequent oil changes has been disputed by a few, not many, people on this forum.
That said, I would have already had my first oil change. The first oil and filter change will get any microscopic particles out of the system, instead of letting them circulate through the system. A new or rebuilt engine will, in the first few miles, circulate microsopic particles and other tiny debris that may be deposited while assembling the engine.
If the car were mine, I would go change it before the trip and then change it when you get to the appropriate leg of the trip. You don't have to take it to an MB dealer to get the oil changed. Keep records of your oil changes, and let the regular service intervals be done and logged at an MB dealer. You can't change the oil too often, it's the cheapest engine insurance you can buy.
One other thing, if you will drain the oil when the engine is hot, more of the contaminants will be removed from the engine. The main reason you change oil is that it is the only means you have for cleaning the inside of the engine.
Change oil hot, and change oil often.
Have a safe and fun trip,
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in