Everett's and Elizabeth's 3 week vacation in Germany.

Given the excellent rail service in Germany, I can't see much benefit in leasing a car for the whole time. Plus, city driving is maddening in many European cities. Plus city parking is difficult and expensive. You might want to restrict your car rental to those areas with scarce or inconvenient public transport. Adding Prague, which deserves several days of its own, onto the Rhine, Bavaria, Munich, and Berlin is a step too far, IMO. You could add a night or 2 in Salzburg between Fussen and Munich.

I agree that taking the train with a pass might be the best idea for Germany; especially if you are planning to visit the cities you mentioned, where a car could be a nuisance because of traffic and expensive parking. And of course you should take a boat on the Rhine. You can book day tours to some castles with transport and admissions that can be convenient and affordable. If you pack light, you will be happy. Three main change of clothes, etc. 2 pairs of water resistant shoes, and coordinated light outer layers. Buy meals to go from Deli and supermarkets. Try to route yourself in a continuous circle to save time not having to back track. You might be able to do a long haul as an overnight on the train if it is possible after Covid.

Forget everything you know about traveling in the US. Europe, particularly Germany, is not the US. Here you need a car almost no matter where you go. It's different in Germany. If you plan, you don't need a car. Trains go almost everywhere. They are fast, efficient, and less expensive than renting a car.

You can easily get from FRA to Bacharach with only a local ticket (RMV, Frankfurt Metro District) on regional trains in just over an hour, for 12,50€/P.

With a non-refundable, advance purchase, SparPreis, ticket, two of you can go from Bacharach to Füssen for only 47€. For 12 euro more, you can get a ticket that is refundable for a voucher up to the day before.

You say you want to go to the Bavarian Alps next, but you don't say where. But once you are in Bavaria, you ( 2 people) can take trains anywhere in Bavaria, all day, for 32€, with a Bayern-Ticket. So go to Garmisch-Partenkirchen, or wherever, next, for 32€. Then to Munich for another 32€.

If you want to go from Munich to Prague, there are Bahn IC buses from Nürnberg that make the trip faster than trains. The advance purchase fare is 45,80€ for two including an ICE from Munich to Nürnberg. These aren't your ordinary city buses, but modern, over-the-road coaches with an attendant and a snack bar. Or you can go by train directly from Munich for 76€ for 2.

We lived in Augsburg, Germany for four years and have been all over that country.

Driving is easy in Germany, except on the autobahn, be sure that you don't just stay in the left lane when faster cars approach you. You MUST move over. Germans follow the rules of the road, but on the autobahn, speed can kill. Some cars will pass you going 120 MPH.

I suggest staying in Garmisch instead of Fussen. Consider going up to the top of the Zugspitze, highest mountain in Germany.

When in the Rhineland, consider visiting Heidelberg and going south to visit the Black Forest (Titisee and Triberg) as well as Strasbourg, France. Strasbourg is interesting since it has been a part of Germany in the past and the people there are a mix of French and German.

North of Frankfurt, consider visiting Rudesheim and taking a short Rhine cruise.

On your way to Bavaria, take the Romantic Road starting from Rothenburg ob der Tauber on down to Garmisch.
https://www.romanticroadgermany.com

3 days in Munich would be a minimum, as well as visiting Berchtesgaden and Salzburg, Austria.

If you want to go from Munich to Prague, there are Bahn IC buses from Nürnberg that make the trip faster than trains. The advance purchase fare is 45,80€ for two including an ICE from Munich to Nürnberg. These aren't your ordinary city buses, but modern, over-the-road coaches with an attendant and a snack bar. Or you can go by train directly from Munich for 76€ for 2.

There are direct buses from Munich to Prague as well, cf. busradar.com (fares for Oct 26, currently limited services due to the corona crisis). Train tickets start from 385 Czech crowns (€14.17) if booked at the web site of Czech Rail.

That's as far as I've gotten with my itenary, Amy ideas?

Rick Steves' itinerary suggestions for Germany are prioritized for the "average tourist" by the number of travel days one has. His 21-day rampage through Germany contains some good destinations, but to include all these places would be an exercise in perpetual motion. I see you have Berlin on your wish list; IMHO you should ignore Rick's fantasy that one can leave Salzburg (or wherever) for Berlin on the morning of Day 8 and finish with Berlin by the end of Day 10. If you choose to go to Berlin (and you don't have to) you should plan on at least 4 full days there.

At least Rick tells you to "slow down" at the very end:

3 days: Munich, Bavarian Alps
5 days, add: Rhine Valley, Rothenburg
7 days, add: More of Bavarian Alps, side-trip to Salzburg
10 days, add: Berlin
14 days, add: Nürnberg, Mosel Valley
15 days, add: Dresden
17 days, add: Baden-Baden, Black Forest, Trier
21 days, add: Würzburg, and slow down

My thoughts:

1.) You are newcomers to European travel - and there's a learning curve to European sightseeing and getting around. For a less stressful time, don't pack your weeks and days too tightly with travel deadlines.

2.) It's also unnecessary to "cover" the whole country geographically from north to south. You could easily spend 3 weeks in just 1-2 of Germany's 16 "Länder" (states) and have a great time. And less ground travel of course helps one stay within a budget.

3.) Don't "adopt" an itinerary or even specific destinations. Go places that look right for you. Like every traveling couple, you and Elizabeth are not "average" - you surely have your own interests and intellectual curiosities, your own activity levels, your own preferences for leisure time... Where are you on the spectrums? Do you live on great food, or on history? Are you museum lovers or haters? Big city people, or nature lovers? Your answers to questions like these should partially guide your destination choices.

4.) For an enjoyable and educational time in Germany, it is really not necessary to focus on the big tourist "hot spots" or the places recommended most strongly by the guidebooks - or to squeeze in as many of those as possible. Lesser known places can be just as enjoyable (or more so.) Looking at Rick's list, I would nominate Nürnberg (and neighbor-city Bamberg,) the Mosel Valley / Trier, and Würzburg (plus surroundings) for your consideration. Each of these would rank higher than Munich on my list of personal preferences.

5.) The Rhine and Bacharach: The Rhine is where you will find a multitude of castles and castle ruins from medieval times (the Füssen area "castles" are actually palaces that are far more modern.) MARKSBURG Castle in Braubach on the Rhine is the real thing - never destroyed - and a must-see if you are really interested in castles. BURG ELTZ (Mosel Valley region) is also outstanding. St. Goar's RHEINFELS Castle is a worthwhile set of ruins with a good museum. BACHARACH is a small, very sedate town with the prettiest old-world buildings on the Rhine. But as a base town, it comes with drawbacks... one of which is train noise (note location of the tracks in photo.) For easier river cruising, closer proximity to castle tours and the Mosel Valley, riverfront lodging/dining, convenient ferry crossings, quieter hotel nights, and more things to see and do, consider basing in attractive Boppard. Nearby St. Goar is a good alternative as well.