Need help with train ticket options in Germany

Frankfurt Airport to Wuerzburg is quickest by ICE, and across two states, so your cheapest fare will be an advance one booked from bahn.com. The cheap fares are strictly limited to specific trains, so make sure you leave enough time for flight delays and time to get through the airport.

The other trips are in Bavaria using local trains, so whether it's cheaper to buy a day Bayern Ticket or pay a single fare depends on the fare and how many people are travelling. The Bayern Ticket is 23 euros for one person, but then only an extra 5 euros for each extra person up to 5.

Another thing that may affect your choice is that the Bayern Ticket will also cover city transport in Munich, which may make a difference if your hotel is a long way from the railway station or if you want to do some sightseeing on the first afternoon.

For travel from Frankfurt to Würzburg I would not buy a price reduced ticket with these restrictions. My advice is buying a normal ticket for the ICE, the route is not long and the ticket costs 39 Euros. With them you have all options and you can relaxed take the next possible train.
Sometimes convenience is also very nice.
From Würzburg to use the Bayern Ticket is a very good offer.

Thanks Philip and Bert for your advice. There are 2 of us traveling. Our hotel in Munich is near the Marienplatz.

Even though you arrival into FRA is not a trans-Atlantic flight, I would not recommend using a train-specific Sparpreis ticket. You'd be at the mercy of the airline and could arrive late.

If you provided a buffer of an hour to protect your ticket against late arrival, you might as well go by regional trains; you'd get there just as quickly. A fare of 8,10€ each will get you from the closer Regionalbahnhof at FRA by S-BAhn to Frankfurt Hbf and then on an RE to Kahl. Kahl is in Bavaria, so a Bayern-Ticket, purchased from an automat at FRA for 28€ for two will cover you the rest of the way to Würzburg on the same RE. Total fare, 44,20€ vs 78€ full fare on the ICE.

For Würzburg to Rothenburg, a Bayern-Ticket, again for 28€ will cover your travel, but if that is your only travel that day, two single trip tickets, for 13,30€ each will cost a little less.

For Rothenburg to Munich, I would use the Bayern-Ticket. Regional trains from Rothenburg to Munich will not take that much more time, and the Bayern-Ticket will be a lot less expensive than the ticket through Nürnberg on the ICE. You might get a train-specific Sparpreis ticket, but at best it will cost about the same as the Bayern-Ticket, but could cost more, depending on how sold out they are.

Thanks Lee! I really appreciate your expertise! Sounds like I should wait and buy all my tickets once I am in Germany.