Need help with this plan!

You might want to reconsider driving immediately after arrival. Lack of sleep, jet lag, and being on unfamiliar ground might not bother some people. Others are driving semi impaired, and others (like me) shouldn't be allowed to operate machinery at all. Don't mean to rain on what sounds like a great trip, just offering food for thought.

Good advice from TC above.

If you want to press onward from Munich upon arrival, then take the train, head for Rothenburg, and spend the night. After a night or two, you will have recovered enough from the jetlag and exhaustion of flying half way around the world, rent your car there, and you'll be in better shape for driving. Besides, you're planning on spending 2 nights there in Rothenburg anyway - you're not going to need or want a car while you're there, it'll just be an expensive headache (you pay for the unnecessary car rental for two days and have to pay to park it, too - taking the train to Rothenburg will save you money as well as perhaps saving you from a car accident).

Great idea to wait on the car! Thank you! Any help with day 8 and 9?

That's a lot of driving. You could breakup the Berchtesgaden to Luzern stretch by going through Austria (Vignette) with possible stops in Innsbruck, St. Anton am Arlberg etc. then Liechtenstein? You did not mention the time of year. Be prepared for Stau in Germany and some boarder checks. Anymore the speed limits on Austrian Autobahns seem limited to 100 kph. If I'm not mistaken you will need a Vignette for Swiss Autobahns too.

Lake Constance ( Bodensee ) - Meersburg would be my choice. Nice castle, nearby Birnau church, Pfahlbauten prehistoric lake dwelling

You have a lot of stops. Are you locked into the dates of the locations you already have? What time is your flight home? Will you need to stay in/near Stuttgart on your last night? I find it's easier for me when planning to go by how many nights I'm in each location. How many nights do you plan in each place? Two nights = one full day, 3 nights = 2 days, etc. Factor in the time it takes to change locations. It will take longer than you think it will.

If you are flexible I would spend at least 2 nights in Colmar, giving you a full day to explore a bit of the area. It is a minimum of a 3 hour drive to Stuttgart from Colmar, plus you need to turn in your car and be at the airport plenty of time before your flight.

Why not start with Berchtesgaden (3 hr train trip from MUC to Berchtesgaden Hbf); you can make the entire trip with a Bayern-Ticket - €42 for all three of you. All the buses in Berchtesgaden are free with the pass you get from you host. The round trip bus from Berchtesgaden to Salzburg is €10,40 pP with an RVO Tagesticket. Then, if you must drive, pick up a car in Freilassing and go to Rothenburg, then to Mittenwald (so you will be closer to Luzern).

There are several nice places between Mittenwald and Luzern. Oberstdorf, in the Oberallgäu, is a nice place, but a little too much like the Berner Oberland. Lindau, on Bodensee, is a lovely island city just off the German lakeshore. From there, if you weren't driving, you could take a boat across the lake to Switzerland to catch your train to Zürich and on to Luzern.

All the places to which you want to go are conveniently connected by train. There is really no need to drive.

Ummm... Rothenburg and Mittenwald are in opposite directions from Munich. Given your desired stops - can you fly into Stuttgart or Frankfort, drive/take the train to Rothenburg ob der Tauber, (nights 1 and 2) and then the drive/train on to Mittenwald, etc.?

I would also suggest breaking the trip down into where you spend your nights, rather than "days." In addition, you should check out Viamichelin.com for driving times and directions (rough ones of course) to get a handle on how much time you will be taking for getting place to place. I think you seem to be spending more time in the car hitting these far flung destinations than you will be seeing most of them. Thus, you don't actually have that many "extra" days.

Examples: Rothenburg ob der Tauber to Mittenwald is a 5-6 hour train trip or half a day drive too - ie.much of Day 3. The train from Salzburg to Lucerne is about 6 1/2 hours, which would occupy all of day 9 even if driving. Interlaken to Colmar is at least 3 1/2 hours by train or car- ie. much of Day 14 .

Overall, if you skip Rothenburg I think you will minimize your travel days while hitting most of the same spots. And almost everything you seem to want to do can be done by train. Remember European rental cars are quite small so consider your luggage space needs too.

From the end of April till mid June 2020 there will be repair works on the eastern part of the runway at Stuttgart airport. Therefore the Delta nonstop flights Stuttgart - Atlanta and vice versa won't be possible. Connecting flights to other European airports are possible.

Oberstdorf/Fischen area or Meersburg (Bodensee) are the most beautiful places between the Swiss and the Bavarian Alps imo. You could hike to the ridiculously beautiful Schrecksee or Seealpsee for a real treat.