A lot of info to digest…

Any particular reason why you don’t want to go with an international phone/data plan? I got the basic package from AT&T for a trip to Berlin, Paris and Rome and didn’t come close to hitting my maximum usage. When you get back, you call and cancel and they will pro-rate your bill for you. Obviously, I don’t know your schedule, but I can’t imagine why you’d use your phone to make lots of calls beyond your hotel.

Missing Berlin is really a shame. It’s one of my favorite European cities. I’d make every effort to get there, even if it means that you have to ditch the car and catch a train/flight from Bavaria. Not going to Berlin is like hitting up France and bypassing Paris IMO.

I hate to say this, because it’s a must, but Fussen is going to be very underwhelming. The castles are hard to get to and they are largely unfinished. Beautiful scenery, but a little disappointing.

Having a car in Salzburg is a hassle. Most of the Aldstadt is in the pedestrian only area. However, I would look into going to Hallstatt as a side trip. Yes, it takes you a little further into Austria, but it’s worth it: http://www.hallstatt.net/home-en-US/

I’m assuming that you know about Nurenburg and the Romantic Road already.