Congratulations! And welcome to the forum.
You are counting days (13-14, I think) but if you are using the trains during the daytime, your travel days will not be filled with rewarding sightseeing but overwhelmed with routine... packing, check-out, transfer, then a substantial train ride, then transfer, check in, unpacking. Find a meal somewhere on the way. The only small-ish train trip on this plan is Nuremberg > Rothenburg (which requires 3 separate trains.)
This plan would demand a whole lot of rigor for the average seasoned citizen who is porting bags packed for nighttime market strolls in December. And the time/energy you spend at the markets leaves less of both for the normal sightseeing that most visitors have in mind for big places like Munich, Vienna, and Prague.
To gain that time, to reduce the travel routine burden you need to shorten the loop of overnight stops. You do not need the trip to Frankfurt. This plan uses just 3 base towns and substitutes Salzburg for Vienna; it streamlines your main train journeys. Side journeys happen WITHOUT luggage and are OPTIONAL - so if you just want to relax in your base town, you can.
- Ar. MUC, direct train into Munich (5 nights; include a daytrip to SALZBURG; another possible day trip to the ALPS or???)
- Direct train to Nuremberg (4 nights; include 2 day trips... to Rothenburg, and to BAMBERG)
- Train to Prague (3 nights)
- Direct train to Freising (1 night, near MUC)
- Fly out MUC
That's 13 nights, but if you actually have 14 nights, you can switch the day trip to Rothenburg to an overnight in the middle of your Nuremberg stay.
At 72, the above is what my wife and I, who've been touring the continent for 5 decades together, would find manageable. The 70+-year-olds I know would find your Plan A more challenging than enjoyable. Heck, even if you two married at 15, it might be a rough go.
This plan would NOT require a railpass. A Month-long Deutschland Ticket (€58 ea.) would work for everything but the journeys between Prague and the border with Germany. Huge savings. And it would also cover subways, trams, buses in Munich, Nuremberg - anywhere in Germany.
https://www.seat61.com/train-travel-in-germany.htm#Deutschlandticket
You do NOT need to book any travel with the D-Ticket. Just get on the train and ride, just like all of Germany does!!