Thanks everyone for the advice. I've booked a car in Dusseldorf to be returned in Freilassing and will spend that night in Salzburg city, before moving to the countryside for the subsequent nights. As for the drive, good to know points of interest on the way are appreciated. We'll visit Audi in Neckarsulm, then drive to Fussen, to base ourselves for two nights. On the drive to Freilassing we'll make stops accordingly. With such limited time, we'll have to save the other stuff for another trip to Germany.