Southern Germany

Nothing wrong with visiting Nuremberg, but most of the city was rebuilt after intense bombing in WWII.
Instead, consider visiting some of the intact Medieval walled towns on The Romantic Road instead.

https://www.romanticroadgermany.com

It's not too hard to see the reason for the popularity - despite the modern roots of the idea, the tour combines the historic cities of Würzburg and Augsburg with the three medieval walled towns of Rothenburg ob der Tauber, Dinkelsbühl and Nördlingen, and then finishes off with the tourist highlights of Neuschwanstein Castle and the Alps.

Let's break your trip down:

Day 1-2: travel days. No sightseeing.
Day 3: Partial travel day. Limited touring.
Day 4: Touring
Day 5: Travel to Nuremburg - some touring
Day 6: Touring
Day 7: Travel, little touring
Day 8: Touring
Day 9: Travel, little sightseeing
Day 10: Return.

Your trip is not 10 days. It is 8 days on the ground. You wish to go to 5 places. This is a lot.

Far better to recognize FOMO (fear of missing out), cut out some locations, and travel less. Day trips are better than full location change.

I'd do 3 stops, 2-3 days each. Cut out the Black Forest. Munich, Nuremburg, Salzburg. I'd actually eliminate Salzburg in favor of some other German town.

Are you renting a car? Another headache. I'd do trains.

Since you live on the east coast, you should not need to buy a Munich round-trip air ticket. It is quite far between the BF and Munich, but Salzburg (for example) is convenient from Munich. You should reorganize your itinerary to eliminate at least ten hours of train time. And you might be able to hit some other interesting places, by flying home from Basel or Zurich. BTW, we take Lufthansa (partner) connections to United often, usually at negligible cost.

This newsboard is very fond of Rothenburg ODT, but I haven't been there. I personally find Munich overrated, but we did like Rick's nearby mountains. Our first KL turned out to be Buchenwald, rather than Dachau.

Beer is a huge part of local culture everywhere in Germany, sometimes to the exclusion of distant styles. You don't have to be in Munich to try beers.

I'm sure I will sound a bit like the others here.

"If there is a reasonable way to consolidate so that we’re switching hotels less but can still see Heddesheim, the Black Forest, castles, the countryside, historic WW II related sites and sample beer, then I am open to it."

Great to hear that you are flexible! It's your first time to see Germany, the things you mentioned in this sentence are a good way to get to know the country, and they can indeed be done in 10 days. So let's get started...

Day 1: Fly into FRANKFURT from Logan Airport. Catch a regional train to Koblenz (just 90 minutes from FRA, the town where Rick Steves begins some of his Germany tours) or better yet to the small Rhine River town just outside Koblenz named BOPPARD. Stay there 4 nights. This is the perfect place for beautiful day trips by train to see the countryside, tour castles and old-world towns, and check out a WW II site...

Burg Eltz (near the nearby Mosel River) and/or Marksburg Castle (in Braubach)

Braubach and Bacharach (old-world towns with half-timbered buildings)

Remagen Bridge WW II Museum (at the site of the former Ludendorff Bridge, where US forces crossed the Rhine)

Rhine River Cruise (only takes 2 hours)

Day 5: Take the train to Heddesheim - You must first travel to a city that is on the way, Mannheim (major train hub) and stow your bags in a locker there. That's 1.5 hours by direct train. Then take a local train to Heddesheim for whatever you have planned there (it's ony 18 minutes from Mannheim.) Later in the day, return to Mannheim for your bags and catch a train to the great little Black Forest town of GENGENBACH. That takes about 1 hour (17:36 - 19:03, for example.) Stay there 2 nights. Besides the beautiful old walled town that is Gengenbach, you can take a short train ride to the Black Forest Open-Air Museum (great place to learn about the Black Forest) and to the town of Triberg which lies high in the mountains of the Black Forest, a trip which uses the scenic Black Forest Railway.

Day 7: Take the train to NUREMBERG and stay there 3 nights. (It's a longer train trip, like 5 hours, so get an early start.) Nuremberg is a major train hub and a fantastic town itself. Of course it was bombed in WW II - like Munich, Berlin, and all the other important German cities! But it has been restored with an eye to its historic pre-war appearance and its smallish old-town zone is both walkable and atmospheric. Nuremberg has a multitude of WW II museums but also a ton of other interesting museums. It also has some good brew pubs. And if you want a day trip from there, BAMBERG, one of Germany's best-preserved old-world towns and world-famous for its beer, is easy to reach in less than an hour.

Day 10: Take an early DIRECT train from Nuremberg to FRA airport (3 hours) if you have an afternoon flight. If you have a morning flight, then don't spend Night #9 in Nuremberg - catch your train to FRA late on Day 9 and spend the night at an airport hotel. While it's possible to fly home from Munich as well, Nuremberg > MUC airport takes close to 3 hours by train anyway, and if the round-trip fare to FRA is better than the multi-city FRA + MUC option, you might as well just fly home from FRA.

You don't need to see Munich just because it's your first trip to Germany. I too find it overrated. And you certainly aren't seeing Germany in Salzburg, so I'd have no qualms at all about dropping these places on this trip and doing your stated priorities instead.

I'm happy to pass on informational links to any of the places I've mentioned above. PM me for those if you wish.

Well, it's your trip, you can do what you want, but you asked for advice. I wouldn't do it that way.

The first place you want to see is Heddesheim. I don't understand why you're so determined to see that small, non-descript town. But flying into Munich, then spending 4 hours plus on the train to get there, while jet lagged, doesn't make a lot of sense to me. Heddesheim is only an hour or so from FRA. If you're so determined to go to Heddesheim, why not fly into FRA?

If you want to see something in the Black Forest, than something else in southern Bavaria, fly open jaw, into FRA, see the BF while you're close, then take one long train trip southern Bavaria, see things there, and fly out of Munich, or vice versa.

Thank you everyone for the feedback.

Fair question about Heddesheim. It’s a family place, and I’ve never been.

I’ll have to investigate any cost difference flying into Frankfurt and out of Munich.

I’m still deciding if and what I’m willing to give up.

There are a lot of good suggestions above and you'll have a great trip regardless of which towns you choose. What is most appealing will be a matter of personal preference. There is a related thread recently on "hidden gems" in Germany that you may want to look at. Many are in southern Germany. https://community.ricksteves.com/travel-forum/germany/article-germany-s-smaller-hidden-gems
My only additional comment is regarding Nuremburg. It's great as a WW2 history stop but not so much if you are seeking the look and feel of what most of us think of as a traditional and picturesque German town. There are plenty of beautiful towns and villages in the same region that were not heavily bombed and are not heavily visited by tourists. Some are mentioned in the replies above and others in the hidden gems thread. Have fun!

Personally I think the Black Forest is overrated unless you want to buy a Cuckoo Clock. You won't be able to get to the best places. In April I would skip it and consolidate your trip from there. Maybe an extra night around Salzburg and the lakes and mountains,

If you have family in Heddesheim, you may want more time there. If it is just the town your forebears came from, I'm less enthused. Having a German friend can make your trip much better.

I guess I don't agree with some here on the forum. I love the northern Black Forest; I've spent 24 nights there in 4 towns. Great spas (Thermen). Same with Munich, the only large town I like; spent 14 nights there (plus 2 in Freising).

I'd skip Nürnberg and Salzburg, spend more time in Munich. Lots of things to see there: Dachau, Deutsches Museum, Marienplatz. Take a side trip to Füssen and the King's "castles", if that appeals to you, or Mittenwald, or Herrenchiemsee. It would also be possible to do a day trip from Munich to Nürnberg.

Before or after Heddesheim, see another BF town. Gengenbach is popular here. Go to Hausach and the Black Forest "Freilicht" Museum. Take the train down the Schwarzwaldbahn to Triberg. Then head for Munich. On the way, if you are interested in authentic castles, stop in Harburg (Schwaben). There is an authentic castle from the middle ages there. Just north of there is an authentic walled city, Nördlingen. Smaller, less touristy than Rothenburg odT (doesn't have a Christmas shop or a Crime & Punishment Museum), but with a Wehrgang you can walk on.

You really don't have that much time in Germany. Go to fewer places and spend more time in them. Don't spend all of your time travelling.

If you want to see more, come back. "Assume you will return." (Rick Steves)