Hope others can give you insight into the places you mentioned above Prague, Vienna and Salzberg, unfortunately I haven't been to them either but have spent the last 29 years visiting Germany, always ending up in Berlin (DH's family), but so many wonderful little spots to check out if you plan to rent a car or use the fantastic transportation system over there. Would you have time to do a Rivers of Europe trip? My friend did that this past year & absolutely loved it, and there were quite a few optional tours along the way as well.