...then 3 nights in Rothenburg...a day trip from there to maybe Nuremberg or Bamberg (too similar to Rothenburg and/or too difficult to get there?)?...and then 4 nights in Munich?
Your enthusiasm for small towns, art/opera and his interest in beer will be better served with some re-organization of your current plan.
Nuremberg and Bamberg are completely distinct from one another and from Rothenburg as well. Rothenburg is a tiny backwater, nearly half destroyed in WW II and rebuilt in the most cutesy/touristy fashion thereafter. It is the smallest of small towns, definitely the smallest of the places you have mentioned. Half a day here is enough for the interesting stuff. The people on the streets are almost exclusively international tourists with some German tourists mixed in, along with the locals who serve them; the town is easily overrun by Easter-time tourists from all over the planet, which is a good thing for the only industry in Rothenburg (tourism.)
tourist map: https://mochilerosdospuntocero.com/wp-content/uploads/2014/07/Rothenburg-Tourist-Map-987x1024.jpg
Nuremberg by comparison is a real city. It has a population of half a million, but since most stuff to see is within the attractive old-town zone, it seems smaller than that and is easy to get around on foot; that said, it's much larger than Rothenburg and offers much, much more to see and do. It is a multifaceted place that feels very different from Rothenburg, very "German" by comparision. Rebuilt after the war, it still evokes the past, despite the fact that it suffered a lot of damage. A couple of days in Nuremberg would not be too long. MANY good pubs in Nuremberg too.
tourist map: https://inuremberg.com/wp-content/uploads/2018/12/nuremberg-city_map-1.jpg
Bamberg (pop. 80,000, only 45 minutes from Nuremberg by direct train) is a UNESCO World Heritage site on the basis of its well-preserved old town, a delightful place for wandering, and maybe the best town for Franconian food/beer/culture. You need close to a full day here.
https://en.bamberg.info/
https://smspostcard3.blogspot.com/2009/07/missing-germany-town-of-bamberg.html
With your interest in the arts, you should not miss out on BAYREUTH (only 55 minutes from Nuremberg.) The Margravial Opera House is outstanding - and also a UNESCO World Heritage site. Maisel's Brewery tour is fun.
Guide for a one-day visit: https://www.bayreuth-tourismus.de/en/discover/the-bayreuth-guide/one-day-in-bayreuth/
The best way to see these places is to spend as many nights as possible in Nuremberg and day trip to the others. Even Munich can be a day trip from Nuremberg if you wish. Regensburg and Würzburg are also a worthwhile day trips from there.
This railway map shows Nuremberg (Nürnberg) to be one of Germany's best railway hubs; Rothenburg, Bamberg, Bayreuth are shown; the other towns mentioned are just a little further out:
https://images.gutefrage.net/media/fragen-antworten/bilder/459443150/0_full.jpg?v=1655930239000
That Rothenburg would make a horrible travel base for these day trips should be obvious from the map - but you can confirm this weakness with a look at the DB train schedules.