Help with trip planning

Someone with more knowledge will surely weigh in on the trains.
What do you mean by "private car"? Are you thinking of renting a car or are you planning to hire a car and driver? IME, renting a car at FRA is pretty inexpensive, even if you add a driver. You don't have to (and maybe can't, I didn't look at the map that closely) drive 100mph on the autobahn in order to get to these places.
In order to know whether 5-7 days is "enough," it would help to know what your interest in these places is. E.g., if you want to do an all-day hike in the Bavarian Alps, well, you need a whole day for that. A first step is to make a list of the things you want to see and do in each place, do some research as to how long these things take, then factor in travel times.

Private car is hiring a driver/car. Things we want to do is do minimal hikes that doesn't require any special equipment or walk around a lake. We were interested in the Christmas Museum in Rothenburg and clocks and waterfall in black forest. otherwise, we are just looking for areas to relax, walk around and maybe do some activities each day or day trips to other areas.

Your destinations are wrong for so little time.
Private transfer would be supremely costly.

You clearly want small, pretty towns with old-world atmosphere. I suggest this plan instead.

1) FRA airport > Würzburg. Direct train, 80 minutes.Get rooms near the station.

• day trip to Rothenburg. 70 mins., 1 chg. of train in Steinach of 13 mins., easy without luggage! Back the same way.
• day trip to Iphofen, old walled town, wine/art emphasis. Direct train, 25 mins. Back the same way. Click on this link for photos (2 pages)...

https://www.stadtbild-deutschland.org/forum/index.php?thread/2985-iphofen-galerie/

2) Train to Mittenwald (gorgeous.) 4.3 hrs, (using 9:03 - 13:23 trip as an example.) 1 chg of train in Munich with a 25-min. layover in Munich. But listen, YOU DO NOT have to catch the connecting train as it's a Regional train... You can have lunch at Munich station and take ANY regional train to Mittenwald that same day.

FORGET the Black Forest. Too far off your track. G-P area is rich with things to do!

Map showing the ample transportation network around G-P:

https://bahnland-bayern.de/files/media/bahnland-bayern/tickets/regio-ticket-bayern/Regio-Ticket%20Werdenfels/2025/beg-gr-gueltigkeitsbereich-regio-ticket-werdenfels-2024-12-ansicht.jpg

Black forest is more for seeing the clocks. Is there somewhere else we can see these? Or go there first and then travel to Rothenburg and then down into the alps

Cuckoo Clocks: Take a long break in Munich (put bags in a station locker) on the way to Mittenwald and check out this shop:

https://www.herrmann-geschenke.de/en/#c288

If budget is no object, then perhaps the private car to Rothenburg is doable.

However the train to Rothenburg is no problem. The time between trains, especially the final one at Steinach, is designed to be doable, and at Steinach the train’s reason to exist is solely to take people to Rothenburg and it will wait for everyone to get on board. If for some reason a train is late - as mine was last visit - just take the next one.

Triberg would be o.k. but I prefer Gengenbach. Triberg is an easy day trip from there. If you do that, get on the bus that meets the train to take you to the center of town. If you wait, perhaps to use the restroom as my wife did, then you will have to walk. Not far, but why do it if you don’t have to ?

I haven’t been to either G-P or Mittenwald.

I think 5 days is too short, 7 should be o.k. since this is part of a longer trip.

Be sure to pack light enough that each of you can manage your luggage without assistance

I'm okay going in whichever direction makes the most sense after arriving into Frankfurt. I just didn't want to have to worry about any complicated or a lot of transfers after flying all night. I will have to look into that town as I love the idea of just traveling to Triburg for the day.

seashell: Bigtyke and I are both very fond of the Black Forest and have both spent lots of time there. Bigtyke is correct about Gengenbach being a fine place to base yourself- and that it's preferrable to Triberg. I have recommended it to others dozens of times myself.

Getting from FRA to Gengenbach should take around 2 hours on with the high-speed train option - you will have one or two changes of train to reach Gengenbach, depending on what time you leave FRA. Not too bad.

That said, the reason I suggested you forget about the Black Forest is the concern that you expressed about transfers. It's a very long journey you will have AFTER your stay in Gengenbach to reach Garmisch/Mittenwald. You will have to ride 4-6 different trains over a period of 7+ hours to make this train trip!

Multiple transfers like this, as anyone who rides trains in Germany these days can tell you, are NOT likely to go smoothly because train delays are very common.

The FRA > Würzburg > Mittenwald itinerary I suggested is quite streamlined by contrast. AND... if you are able to visit Rothenburg and Iphofen from Würzburg, as suggested, you'll be able to see some old walled towns that are similar to Gengenbach. The FRA > Würzburg > Mittenwald itinerary is probably not the only option.... but the FRA > Gengenbach > Mittenwald option is precarious and simply cannot be streamlined into a trip of reasonable length.

Please, before booking accommodations, please have a look at the train journeys yourself at the DB site so that you feel fully informed about what you will be undertaking.

Honestly, IMO that itinerary is not super realistic even in 7 days. You've picked fine, but really poorly connected destinations. And really...on that short of a trip, jet lag and transfers make such an outsized impact. You're spending so much time on trains vs seeing things. That's awesome in the Alps, but not awesome otherwise.

If you're just interested in cuckoo clocks, you can see those a lot more convenient places. Even in the Black Forest, much of the stuff is made in Vietnam or China. On your short itinerary, the Black Forest doesn't work really.

Maybe look at just basing in Munich or Salzburg. Both are awesome and have good day trips. Both are better connected for Italy.

Alternatively, try to add some time to your trip??

Trains are super easy, comfortable and a great way to get between cities. Don't stress. Pack light "like carryon that you can lift" light. Don't bring more than 2 pairs of shoes, focus on a "color capsule" for your wardrobe so you can mix/match. There are a hundred other tips but the importance of packing light cannot be understated. It is ultimately freeing. If you pack light, it'll help you make those connections. You just need to get on the train. Once on, you can find your car and your seat.

I have the rest of our trip through Italy dialed in. Germany I'm having a harder time with the trains. We might just need to drop Rothenburg and stay in an area of the black forest instead and then move to the alps and stay. I'm okay with one long train ride over 4 hours for this part of the trip.

I'm okay with one long train ride over 4 hours for this part of the trip.

G-Bach > Mittenwald isn't just "over 4 hours." It's a 7-hr. journey on 4-5 different train, with multiple transfers and short ones at times. It's just the kind of train trip you said you were hoping to avoid.

Germany I'm having a harder time with the trains. With the above itinerary, yes, it looks like a hard time. The alternative plan with Rothenburg had a much more accommodating train schedule.

You cannot buy train tickets now for next summer. You still have a lot of time to revise your current plan. If you are set on the Black Forest and on dropping Rothenburg, fine with me; you can still avoid that long train trip to M'wald in other ways, maybe 5-6 different ways. Perhaps take a stopover night somewhere interesting in between. Sigmaringen might be worth a look. We were there last year. Karls Hotel (top notch!) there has a view across the Danube to Sigmaringen Castle:

https://img.fotocommunity.com/sigmaringen-schloss-706f396f-55f2-4ed0-ae8f-fbf0b447e4db.jpg?height=1080

If you are truly OK with an all-day train trip and multiple changes of train, you could in fact spend more time in the Black Forest... area it's a lovely place to explore ... and then head straight to Italy from there, bypassing Mittenwald. Bolzano is only a couple of hours more from G'bach, with no extra transfers.

Or re-route via Switzerland, taking the Arlberg route to Innsbruck on the way to Italy.

https://www.seat61.com/trains-and-routes/zurich-to-innsbruck-via-the-arlberg-railway.htm

There are plenty of towns like Rothenburg, towns that are original, not rebuilt, with walls and towers and medieval centers. Take a look at Büdingen which is only an hour train ride from Frankfurt.
https://www.buedingen.info/

Or try Idstein, Seligenstadt, Marburg or Limburg for that medieval feel.

Just that I read your post: What used to be the largest cuckoo clock is standing in Wiesbaden near Frankfurt (easy train ride of 30-50 minutes).

No worries about transfers: If you miss because you arrived late, you can take the next one.

Looking your itinerary, I feel that combining Rothenburg, Black Forest and Bavarian Alps is the biggest obstacle, as it is a nasty zig zag. I would recommend doing either Black Forest and swiss alps on the way to Italy, or Rothenburg and Bavarian alps. Regardless of your choice, you will be able to replace the other with a nice but more convenient alternative.

There is more to see in the Black Forest than Cuckoo Clocks. You might find it too far from your Rhine sight seeing excursions in the short time you will be in Germany but for future reference the transportation there is excellent and you can ride a train or take a bus to most trailheads. If you don't care to hike you can visit this charming museum, Vogtsbauerhöfe, that is actually a village of 200 year old houses and gardens. https://www.youtube.com/watch?v=boqxA7RhxRA