Eugene,

while you are working on your itinerary this weekend, understand that the Bayern ticket is valid anywhere in Bavaria, including into the station at Salzburg.

If you use it from Rothenburg or Nuernberg, it will also be valid for all the conveyance (S/U-bahn, streetcars, buses) in Munich when you get there.

If you use it to go to Fuessen, all the trains to there are regional, so it won't take you anymore travel time. There is an issue with the 9 AM start time since the trains leave at 8:52 and 9:51. but, you can take the 8:52 with an additional €8,80 single MVV fare to Geltendorf. That is still less than full fare.