question on trains within Bavaria

A Bayern Ticket (only exists as a daily version as far as I know) is definitely worth it to go from Munich to Rothenburg odT.
Do mind that it does not let you take trains before 9am from Mon-Fri, which might be restrictive to go to Füssen.

thanks so much for another helpful response balso, I already bought the castle tickets taking into account the 9 AM starting time. I bought the Hohenschwangau ticket for 1:40 PM and the Neuschwanstein for 4:45 PM. What would you advise? Wait until 9 for the Bayern ticket to kick in or just go to fussen earlier and have more time in the actual town, maybe do the walk from the town to the castles?

The Bayern Ticket will be valid not just to Füssen but also on the bus to the "Neuschwanstein Castles, Schwangau" bus stop. Might as well take the bus as walk. No need to rush there out of Munich that morning just so you can do that walk. You'll have a strenuous walk from the bus stop to the N'stein entrance to contend with anyway.

Rothenburg (check your spelling) to Nuremberg can be done more cheaply (€21.50 / 1 person) and without the 9 am weekday restriction if you purchase the VGN Tagesticket Plus instead of the Bayern Ticket. Note that this day pass also gets you on trams, buses, and subways within Nuremberg on the same day. If you happen to buy it on a SATURDAY, the VGN Tagesticket Plus is valid not just for Saturday but Sunday as well... use the inner-city transportation that day, or take a half-day trip to some other place if you wish.

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

Russ, thanks so much for letting me know about the VGN Tagesticket Plus. I never would have known about it without you! I'll definitely be using that. The Rothenburg to Nuremberg day is planned for a Sunday. Do you happen to know which letter "price level" I need for the Rothenburg-Nuremberg trip?

ok, so it seems like I should get a bayern ticket for the day trip to the castles and another one for the munich to rothenburg train day and then the VGN Tagesticket Plus for the Rothernburg to Nuremberg day.

The bayern ticket is something you buy day of right? No need for reservations so then I can take any Munich-Rothenburg train I want as long as it's after 9 AM?

Thanks again everyone

Just buy at the maximum price level for that ticket. Only shorter distances than you will be traveling cost less.

Leave at any hour you like on your R'burg > N'berg trip.

Buy all tickets at the station on the day of travel; reservations are generally not possible on the regional trains which you will be using anyway.

"I can take any Munich-Rothenburg train I want as long as it's after 9 AM?"

NO. Only regional trains are eligible for the Bayern Ticket and similar day passes around Germany.

The Munich > Rothenburg route is partially served by certain long-distance trains (IC, ICE, EC, etc.) which are NOT eligible for use with the Bayern Ticket. To avoid boarding any of these, all you need to do is check the "only local transport" box under "means of transport" when you search down itineraries at the DB site; those ineligible trains will be eliminated from the results:

https://reiseauskunft.bahn.de/bin/query.exe/en

Once you have itineraries on the eligible trains, click on "show details" to find your routing, changes of train, platform numbers, etc.

Munich-Rothenburg: There is a single long-distance train a day between Munich and Steinach near Rothenburg (IC 2082, Munich East-Hamburg, departure 11:17, dep. Munich-Pasing 11:30). It's not particularly fast (because it is sitting for half an hour in the station of Augsburg waiting for the train from Oberstdorf), but it saves changing trains in the large station of Nuremberg (you always have to change in Steinach) and is cheaper than a Bayernticket if you travel alone and if you book early. In early May, for example, €19.90 p.p. (or €15.40, if you book Munich-Steinach for 12.90 and add a €2.50 VGN ticket for the Steinach-Rothenburg leg), whereas the Bayern ticket costs €26.

Do you happen to know which letter "price level" I need for the Rothenburg-Nuremberg trip?

What you need is a "Tagesticket Plus", price level 10.

The Munich > Rothenburg ticket sla019 recommends is called a "saver fare." These tickets will rise in price as tickets sell, so book early if you want that. Keep in mind that saver fares come with a "train-specific" condition - you must ride the specific long-distance train that you are pre-scheduled for, so with that IC train, there's no being late (or you forfeit the ticket) and no flexibility (for stopovers, etc.) like you'd have with the Bayern Tickets. Saver fares can sometimes be refunded in advance, but refunds come with penalties.

sla019 and russ, thanks for the info on the saver ticket. It seems like for me it may not be worth the money saved.
So to repeat, for Munich day trip to castles, Munich to Rothenburg, and Rothenburg to Nuremberg, I'll buy all tickets at the station on the day of travel and use the bayern ticket for the first two and the VGN Tagesticket Plus for Rothenburg-Nuremberg. It's nice to not have to worry about tickets and have flexibility (outside of leaving after 9 AM for the bayern ticket).

Munich-Rothenburg: There is a single long-distance train a day between
Munich and Steinach near Rothenburg (IC 2082, Munich East-Hamburg,
departure 11:17, dep. Munich-Pasing 11:30). It's not particularly fast
(because it is sitting for half an hour in the station of Augsburg
waiting for the train from Oberstdorf)

@SLA, isn't that the train they call the Alpine Express (or used to)? The northbound train comes up from Berchtesgaden AND Oberstdorf and combines in Augsburg (maybe that's why the delay), continuing via Steinach up to northern Germany. We used it in 2002 to get from Freilassing to Berchtesgaden. It runs as an IC from Augsburg to Freilassing, but then changes designation to an RE for the run down to Berchtesgaden. Since it is an RE for that stretch, we were able to use it with a Bayern-Ticket. Unlike an RB, which feels like it's bouncing down the track, the IC (being a deluxe, long distance train), just seemed to float along.

The Bayern-Ticket would include all of your transportation, from anywhere in the 'M' (downtown) zone in Munich after 9:00 on a workday, by bus, S/U-Bahn, or tram to the Munich Hbf, from the Hbf by regional train to the Füssen Bhf, and the bus from Füssen Bhf to near the ticket kiosk in Hohenschwangau, plus from there back to your starting point in Munich.

However, you mentioned possibly wanting to go earlier than 9:25 (Arr. Hohenschwangau at 12:20). But to take the 8:40 (arr. Hohenschwangau at 11:20) , you could not start using the Bayern-Ticket before 9 AM. Full fare for the trip using the earlier 8:40 RB is 29,10€ (for 1), and that 1) does not cover transportation to get to the Hbf in Munich or the nominal bus fare from Füssen Bhf to the castles, and 2) is only to Füssen. You would still have to buy the return trip ticket, which could be a Bayern-Ticket anyway, to get back to Munich.

But the RB that leaves the Hbf at 8:40 gets to Geltendorf at 9:07; from there on you could use the Bayern-Ticket the rest of the day. An MVV single trip ticket to Geltendorf from anywhere in the 'M' area is 10,50€/P, and you can use the MVV ticket at any tine. So, you could buy a Bayern-Ticket and an MVV ticket to Geltendorf and get on the 8:40 RB. When you got to Geltendorf at 9:07, you could start using the Bayern-Ticket, and you would get to Füssen Bhf (not the ticket kiosk) at 10:41, or the bus stop below the ticket kiosk at 11:20.

@SLA, isn't that the train they call the Alpine Express (or used to)? The northbound train comes up from Berchtesgaden AND Oberstdorf and combines in Augsburg (maybe that's why the delay), continuing via Steinach up to northern Germany.

@Lee, I have never heard this name for this train. Among railroaders, it has the nick name "Kukidentexpress" because it is mainly used by pensioners traveling from northern Germany to the mountains (Kukident is a popular brand for cleaning dentures). ;)

(And because I have the right age in the meantime, I am also allowed to use that train from time to time).