advice for German plan

First, be carefull with the exact writing, otherwise you could end up in any village you never wanted to be.
For example:
are you asking about RothenbErg or RothenbUrg? Or are you meaning SalzbErg or SalzbUrg?
So, to give you good answers I have more questions:
why so many days at Bacharach? What do you want to do there?
Why going to Rothenburg and then back to Baden-Baden? This detour doesn't make sense. And you have it planned again on day 20?????

That's too much time in Bacharach- it's tiny. I know, RS likes it, but we did it in half a day . Also, other towns have better transportation access. I'd recommend staying in Boppard, which is charming and has a nice river buzz.
I do like Rothenburg ob der Tauber, and enjoy the nights and mornings in this charming medieval town. We usually put it in the middle of our trips, as it's a nice location to slow down and relax.
Fussen is a tourist trap, IMHO. You can Search and research here on the Forum.
Wishing you a great trip, safe travels!

Regarding tickets, German Rails ( germanrails.com ) is a third party website. They are an approved partner of the German national railway, Deutsche Bahn. For individual tickets though, I prefer using Deutsche Bahn, their App is handy and easy to use, not sure if GermanRails offers any additional benefit.

Lately I have been using the Deutschland Ticket, it covers all regional trains, including to Salzburg, as well as local buses, trams, S and U Bahns (like within Munich). It may not be as great a benefit to you since probably ICE trains between Munich, Nurnberg, and Berlin make more sense, but for Munich-Salzburg twice, around Munich, to Rothenberg and back, that may be enough to pay for it.

As stated perviously, Deutsche Bahn operates, I believe, all of the trains you'll be taking. Book directly with them. Why involve a third party when you don't have to?

I use DB's app. Both that, and their website, are available in English. Easy to use.

I previously provided some specific feedback on this itinerary - see my comments on your other thread.

4 days is not too much for the Rhine/Mosel region. As Pat has suggested, Bacharach is not the best base for a 4-night stay. I entirely agree with Pat's suggestion that you stay in Boppard instead where you will have a much wider choice of hotels (including some with river views) and restaurants as well as the Rhines's coolest chairlift ride. Boppard's innkeepers will provide you a Guest Ticket for free train travel in this area: https://www.boppard-tourismus.de/en/accommodation/

Munich > Rothenburg > Munich on Day 20 is not a doable day trip. You should instead move to Nürnberg on Day 20. Then do your day trip to Rothenburg from Nürnberg on Day 21 or 22. You can use the cheap Tagesticket Plus to get there and back from N'berg.

https://www.vgn.de/en/tickets/all-day-ticket-plus/

Baden-Baden is about casinos and spa treatments. It is too far north to use as a base for touring the Black Forest. I suggest you book Nights 5-6 in GENGENBACH instead, an old walled town like Rothenburg. (Or stay in Baden Baden if you prefer the gambling and the spa stuff.) Yes, make a stop in Heidelberg for a few hours on your way to Gengenbach. I'd actually add one night to Gengenbach if possible. Gengenbach is one of the Black Forest Towns which issues a free Guest Ticket for free train travel all around the Black Forest.

https://www.youtube.com/watch?v=KkgzMXQ7blQ

https://bw.tourismusnetzwerk.info/wp-content/uploads/2019/05/KONUS-Flyer-PDF-Download_GB.pdf

8 Alps - Lake Constance
9 Alps - Lake Constance
10 Alps - Lake Constance

I have no idea what this part is about. or what you plan to do there. There are things you can do there, but what do you have in mind? Bicycling? It's nice and flat there for scenic biking around the lake. Lake Constance is not in the Alps. If you want to visit the Swiss Alps, it's best to continue from Freiburg south into Switzerland through Basel and on to the Bernese Oberland (Bern/Interlaken/Lauterbrunnen etc.) where the Alps are truly spectacular.

like Russ I am confused by

8,9,10 Alps - Lake Constance

I can't get my head around this.

The two are hours apart. What did you have in mind for those three days?

I will disagee. 4 nights is not too long in Bacharach ! I will be spending 6 nights this year, my 6th visit since 2011. Have you a place to stay ? I recommend Irmgard Orth’s 3 room b&b. I’m not sure where you would park the car. A place with parking and in a very picturesque location is Hotel Pension Im Malerwinkel