I think "active but realistic" is a great description of your itinerary. You will be on the go, and will need to do lots of advance research to pick your own personal "must sees," as you will only have time for a taste of each city.
I haven't been to Salzburg, but it is smaller than your other cities, so if you need more time elsewhere, you can probably cut a day there.
If you're interested at all in German history, you will want to budget as much time as you can for the German History Museum in Berlin. If you are interested specifically in Cold War and Berlin Wall history, I think there are two sights that are better than the Checkpoint Charlie museum: the DDR Museum and the Berlin Wall Memorial near Nordbahnhof Station (there's a great exhibit in the station itself about the "ghost stations" and escapes through them, and then you see several free movies about the Wall, then see the only existing section that shows the "double wall" construction).
You will also probably want to take some walking tours in Berlin and Munich, to learn more about the history than you can see just looking at the building exteriors. For instance, the building in Munich where Hitler joined the Nazi Party still stands, but I only learned this by taking a "Nazi Sights" walk. I took two walks in Vienna; one was good, but the one guided by Brigitte Timmermann was outstanding. If I return, I'd take whatever walk she was leading, regardless of subject (she is the one who did the research for the Third Man walk and book). Almost any walk in Berlin will be laden with history, so you can take your pick (Nazi period, Cold War period, Jewish life, gay life, etc).
Here are links to Berlin Walks, Vienna Walks, and Munich Walks. Of course, there are other companies. But beware of the "free" tours, which can be bigger on entertainment than history.