You will get all sorts of opinions when it comes to oil type and change intervals on this forum. My recommendations are:

1. Find a good indy and have him go through the car. Service interval II at the dealer is a big hit to your wallet for a simple oil change.
2. I change my oil every 7.5K miles with a synthetic and OEM filter. Depending on your driving style, you can stretch it more miles.
3. I doubt Carmax changed the tranny fluid with ESSO that is required by BMW since it is so expensive. Even though BMW calls it "lifetime" fluid, there are numerous stories of tranny failure before 100K miles. Most agree to change the tranny and transfer cases at 60K miles or leave it alone if it's gone 100K+ miles.
4. The weak link on the 4.4 is the cooling system, so check all the hoses, valley pan gasket, expansion tank and flush the coolant. Plan on replacing the water pump and thermostat around 100K miles.
5. Flush the brake fluid. It's almost always overlooked on the maintenance schedule.
6. Did I mention to find a good indy ............

Post some pics of your new X ......