I brought a car the other way in 1982 (bought German-spec Audi and brought it to US). A lot might have changed, but I remember a few of the differences were the side-mounted turn signals (just in front of the mirrors) and the parking lights (when you turned the car off with the turn signal on, that side blinker would stay on dimly so the car could be seen on a dark road).
I would research the matter carefully before paying to ship the car over there. Germany has very strict motor vehicle laws, and you'll want to make sure you're able to comply with all of them. Do you have any aftermarket accessories on the car? German vehicles are regulated by TUV, their regulating body, and all automotive parts and accessories- even owner-added- are required to be TUV-approved. There are also other laws that seem draconian by our standards, such as the fact that driving a vehicle with any collision damage is forbidden.
I'm not sure if the German laws cut you any slack if you are an expat. They might, since (at least in '82), foreigners were issued special oval license plates instead of the German rectangular ones, and you could get away with a little more as an 'auslander' if you were pulled over. That might have all changed, so again I'd research it.
I would get in touch with the local German consulate. They should have information on what you need to do.
Good luck! It will be cool to have a Mustang over there. American cars always get a lot of looks since there aren't too many of them over there.