Umm, so whose is the 2010 model X5 in the garage? The Tooth Fairy's?
Dude, if you are serious in saying that this is going to be your first car, why would anyone in their right mind sell an E39 M5 to a first car owner... You'll kill the car, yourself, or both. No offense intended, but you need to be realistic.
Something about your post doesn't "smell" right.