Munich-Prague-Vienna-Interlaken/Gimmelwald

Vienna to Zurich is an 8 hour train ride, so yes, flying might be warranted. But don't rent a car to get to Gimmelwald, it will sit in the paid parking lot in the valley while you frolic in the car-free village. Take the train. There is a train station right at the airport.

If you're flying home from Zurich, then your last night should be in Luzern. Easy and quick connection to the Zurich airport.

I don't know if it's just cheaper to fly into Munich than Prague or Vienna, but you are back-tracking with your itinerary. We spent four nights in Munich last September (with attending Oktoberfest) and thought that seemed like enough time, though most things were shut down on Sunday. We were also in the Berner Oberland for four nights, staying up in Murren, and thought that was also the right amount of time to explore the area (though we didn't do any long hiking, that was just trying to see the highlights). You won't need a car in either place, unless you want to day trip out of Munich into the countryside (we stayed in Lucerne and Fussen in between the Berner Oberland and Munich).

Munich and Vienna are great European cities worthy of 4 days each to properly take in the popular travel sights. Prague is a 3 day city that's not too easy to get to from Munich. And where you're wanting to go in Switzerland is in the middle of this very mountainous country. We prefer travel in Western Tirol in Austria for great vistas of The Alps--and much cheaper and easier to get to than Switzerland.
I agree that open jaw tickets are better even if starting out in the farthest city is a little more expensive to get to. Backtracking is expensive, and the distance from Vienna to Interlaken is pretty far.
I'd prefer flying into Vienna and out of Munich--stopping at Salzburg on the train ride between the cities. You could rent a car in Munich and make a southern loop through Bavaria and Tirol in Austria and back into Munich. We've made that trip a number of times, and never get tired of the incredible scenery in the region.

You'll find beautiful Alpine scenery one hour south of Munich or ninety minutes west of Vienna. Why waste an entire day of your valuable vacation time backtracking to Switzerland?

Thanks, everyone, appreciate the feedback. I hear what you're saying. Switzerland is probably the most important place for us to visit on this trip, but I understand it might not be the most convenient based on our other cities of Prague and Vienna that we want to try to make work.