Thanks to everyone sending a reply. However, I'm surprised that there are minimal responses. I am still trying to as much input as possible to get some sort of guideline for taking care of my 98 E-320.
I suppose it's difficult to get a general oil change interval(mileage, time) since it depends on driving style, trip, climate etc..
From Mr. Myarmar response, it seems that the FSS works fine. However, my car is out of warranty so I don't think I will follow it totally.
I think I'll follow my original plan and change my M1 10W30 oil at 5000-6000 mile interval as my car holds 8.5 quarts of oil (so I don't believe it needs to be change at 3000 which is usually for 4-5 quart of dino oil). If it goes well for a while, I think I will extend it to 7500.