We just returned from the trip. It was fun but with some drawbacks. Accommodations in Trendelburg were problematic at best. That was clearly the low point and with the trip cut to one night there and one more night in Munich, that change is a very big positive. Christmas day in Rothenburg will be fun. Jennae should be one of your guides and she is great. You should have two days of four hour bus rides, be patient. Dress warmly, Neuschwanstein will be cold, but should be very beautiful.
A valuable tip, in Rothenburg, the Kathe Wohlfahrt stores are everywhere (many are not label as such). If you have purchased and shipping from one of their stores and are buying and shipping from another of their stores, show the cashier your prior shipping receipt BEFORE SHE RINGS UP ANOTHER RECEIPT. They will combine the shipping and save you duplicate charges.