Thats a quick trip to hit so many big cities, but it sounds fun. A little advice on Germany- most everything closes on Sundays (except for some cafes and restaurants). So if you plan on doing any shopping in Munich, do it on Sat.
I've been to Munich a few times and would recommend going to some of the museums there (if museums are your thing). And a day trip to Salzburg is easy to do and possibly something to do on Sun. They have a large castle there thats interesting to visit. Also, the Christmas markets will be open in Austria before Germany (and those are open on Sunday) so it might be worth a visit.