I'd consider tweaking David's plan -
There's enough for 2-3 full days in Vienna, especially if you like art museums and parks. Then there are day trips to Melk and to Bratislava.
I don't think Hallstatt rates the time and effort to get there. I visited on an RS tour and it was chock-full of tourists in early June, seems that it has become too popular. I'd use those 2 days for more Netherlands.
There are things to do around Salzburg - Berchtesgaden for the Konigsee (scenic lake) and the Eagle's Nest, with the Documentation Center and Hitler's bunkers. You'd probably need 2 days to see both, not so much because they each take a full day but because of the public transportation connections. There's also a very good outdoor Salzburger Freilichtmuseum in the other direction.
Munich was a let-down for me. 4 nights would be two too many for me.
Switzerland - I've heard that Zurich is not a good tourist destination. Instead consider spending time in the Bernese Oberland/Lauterbrunnen Valley, 3-4 nights to enjoy the Alpine peaks and villages.
There's a lot to see in the Netherlands after Amsterdam.
Too many places, too little time . . . sigh. Sounds like a great trip.