The maximum mileage you will get from your car is an unknown. But if you're going to change your oil and filter as often as you say, I'll bet this car has a pleasant surprise in store for you over the next few years. Frequent oil changes and TLC will make it go almost forever.
Change oil hot, and change oil often,
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in