Time of year makes a difference. Germany is cold by mid-October. Venice is great in late October but hot earlier. I know people who visit Venice with the crowds of summer and are very disappointed. I was there the last week or so of October and it was magic.
Berlin is fine. Bear in mind you will be jetlagged and may not get a lot out of your first day. Berlin is also out of the way from the rest of Germany. If it's important for seeing some family history, that's a priority for your trip.
Munich. I'd suggest three full days there plus another in Salzburg. Salzburg is a quick and easy train ride from Munich. It's a beautiful city, one of my favorites, but it's a small walkable town that can be explored in one full day (a second day is nice but not absolutely necessary). Essentially travel day into Munich stay, tour day, stay, tour day, stay, tour day, stay (unless you are ready to move on then add an afternoon train to Salzburg and stay there), early train to Salzburg, tour day, stay, maybe a second tour day, then move on the next morning.
Innsbruck isn't really a place you need to stop unless it's a ski vacation.
I did similar going from Munich/Salzburg to Venice with a leased car. We stopped in Hall in Tyrol for a lunch and look around, then again in Verona for two nights before continuing to Venice. I'd suggest Verona as a much more interesting stop than Innsbruck. Another option, with a car, is a drive through the Dolomites on the way to Venice.
I took a car into Venice. if I did it again, I'd change to parking somewhere on the mainland (not the closest train stop) and train into Venice. That would have saved me both time and money. If you are going mostly by train, that won't matter.