Lets see:
Day 1, Munich, arrive 2pm
2 Munich
3 Munich
4 Munich
5 Train to Vienna (4 hours), arrive hotel no earlier than 2pm
6 Vienna
7 Vienna
8 Train to Prague (4 hours), arrive hotel no earlier than 2pm
9 Prague
10 Prague
11 Train to Nuremberg (3 hours), arrive hotel no earlier than 3pm
12 Nuremberg
13 Train to Rothenburg (1.5 hours), arrive hotel no earlier than noon
14 Rothenburg
15 Rothenburg
16 Rothenburg
17 Train to Frankfurt (3 hours), arrive hotel no later than noon.
Sure, doable. Not sure of the attraction of some of these stops, but its not too hurried for most folks. I would price tickets independently, I bet you save money if you buy 30 days + early.
Hopefully Ms Jo chimes in on the Frankfurt part of the journey. If she doesn’t, then PM here and ask. Real dates will help some too. You will get more detailed suggestions.
If this is for Christmas Markets, then google "best christmas markets in Europe" and you will get a half dozen good lists to look at. Then maybe rethink your stops .... or not.
For those long walks in Rothenburg, if it is 15 December the average is 33F to 38F for a high. The possiblity including the 10% bands is about 27F to 47F. Dress warm. Oh and there is will be a 26% chance of rain and 80% chance of overcast skies. But you wont see the overcast skies, much, because the sun sets at about 4:15pm. Having said all of that. If Rothenburg interested me, I would go. Its wineter, so what, have fun.