Yes Bus, RE means you take a bus to catch a Regional train, on which the Bavaria Pass will be good. You can buy the passes in machines at any train station in Germany i believe - you need not be in Bavaria to do so. The newer machines will do it - sell Lander tickets for all over Germany - the older style may not

Of course if you buy it at a station before taking the bus then the bus would be covered as well.

Are there signs in Munich airport that direct where to catch the bus to the train station? I'm guessing the bus goes to freising, which someone noted above? Thanks!

>I did a search on bahn.de MUC to Nurnberg hbf and I see one train departing at 9:40 arriving in Nurnberg at 12:25 with one change - on Bus,RE.

If you click on the connection you will see the details. No need to guess...

>I'm assuming this is the only one that leaves around the time we are looking for. Are we able to buy the bayern ticket at the airport?

Since the airport has a railway station you will be of course able to buy any rail tickets there, including Bayern-Ticket.

>Does Bus, RE mean that we take a bus then a train?

As mentioned, just click on the connection you like and you will see the details - which bus, which train, where and when to change...

>Am I to assume that I can buy the bayern ticket wherever the bus drops us off before we jump on the train?

You don´t need to buy the Bayern Ticket in Freising (I assume without looking up that this would be Freising) - by buying at the airport you save yourself the bus ticket.

>Are there signs in Munich airport that direct where to catch the bus to the train station? I'm guessing the bus goes to freising, which someone noted above?

All airports (at least all in Europe that I have been to) have signs directing you. Just follow the bus signs, or ask at the information desk.

Why take a taxi from MUC to Munich - why not Ingolstadt to catch ICE trains to Nurembourg there - paying less for the train?

Scouring the bahn.de site i see no MUC-Nuremburg trains with any bus connection - All seem to go S-Bahn to Munich-Ost station and then Munich Hbf

Can transfer at Ost for regional trains to Nuremburg or at Hbf for ICE trains?

>Scouring the bahn.de site i see no MUC-Nuremburg trains with any bus connection

You have to choose "only regional transport" option, then you will see it.