Reasonable? That really depends on how you want to spend your time. I think it's alright.
I would probably subtract 1 day from Days 2-7 and base in one town or the other (if you base in Berchtesgaden, you get free local transport and a beautiful location that's more alpine than urban; Salzburg is an easy day trip from B'gaden and you get a discount on the trip with that visitors card.) I suppose this would mean cutting Hallstatt. Don't get me wrong, it's a picture-postcard town, but it does require a good bit of time to get there and back to Salzburg - like 4.5 - 5.0 hours, and once you get there, there isn't all that much to do. I think you'll find the Königssee (B'gaden) and the Füssen area scenery equally breathtaking.
What to do with the saved extra day... depends on your interests, of course. Right now you have just a day trip for Nuremberg. That might be a bit snug. I'm going to suggest that you spend your full day there as planned, doing whatever you have in mind. But travel there on the evening of your 3rd day in Munich and stay the night (thus 2 nights in Munich + 1 day of Munich sightseeing on your Day 12.) You wake up in Nuremberg for a full day there and spend a 2nd night there. Now for the saved day... two excellent options would put you in a true old-world German town:
BAMBERG (a UNESCO World Heritage site for it's well-preserved old town, less than 1 hour from Nuremberg; plan on most of a day.)
IPHOFEN (a small, picturesque old walled town with an art/wine emphasis; doesn't require a full day, about 45 min.'s from Nuremberg.)
You can return that night from either town to Munich by train. Bamberg station has lockers for bags. Iphofen doesn't have station lockers, so leave bags at Nuremberg station then fetch them during your layover there as you travel to Munich.
A 3rd option would be Bad Windsheim's excellent open-air museum, the Freilandmuseum - also an easy day trip from N'berg.
