German Train tickets

Yes, The Bayern ticket is as described. Info page (in English) here: https://www.bahn.de/p_en/view/offers/national/regional/laender-tickets/bavaria-ticket.shtml
Validity map (German only) here: https://www.bahn.de/p/view/mdb/pv/deutschland_erleben/allgemein/tickets/pdfs_laender-tickets/2015/mdb_190311_streckenkarte_bay_2015.pdf
As you can see, it stretches over the border to Salzburg. The only catches are (1) From Monday to Friday it is only valid after 09:00, no restriction Saturdays and Sundays (2) Not valid on IC or ICE trains, only "local" trains.

There is no discount for advance purchase of these tickets (Länder tickets), so just buy at the station on the day or before (make sure you select the correct date for future tickets). But, there is a surcharge of €2 for buying these tickets from a manned ticket counter, use the machine instead.

The price of the Bayern-Ticket from a ticket automat is 23€ for the first person plus 5€ (not 4€) for each additional person up to 5, total.

There are two applications of the Bayern-Ticket (and most, if not all, other Länder-Tickets).
1) You can take up to five people, of any age, at 23€ for the first person, 5€ each additional person,
2) OR, the first person can take all of his/her children/grandchildren under 15 for 23€. One other person, either the first person's spouse, or a child/grandchild over 14, or just a friend, can come along for an additonal 5€, but does not get to bring along all their children/grandchildren.

In other words, you cannot buy a Bayern-Ticket for 3 to 5 people AND one person brings along all their children/grandchildren free.

A while back someone posted on RS incensed that he was told by the conductor that he could not bring him, his wife and all of their children under 15 AND one child over 14 on the same 3 person Bayern-Ticket. The description on the German Rail website is a little vague and could be interpreted his way or the right way. The AGB (in German), however, is not vague.

Travel from Freilassing on the rail line across the river into Salzburg is included in the Bayern-Ticket because German Rail built that short length of track to the Salzburg Hbf. Transport within Salzburg is not included with the Bayern-Ticket.

With the multi-day Munich pass, you cannot skip a day (well, you can, but you pay for it anyway). From the MVV website, the validity period of the 3-day ticket is "From the moment of validation until 6 am on the fourth day".

The Bayern Ticket also cannot be used between Munich and Salzberg on Railjet trains, which are the highest class of Austrian express service.

The trains on the Salzburg to Munich line (in fact on other lines in Bavaria) for which the Bayern-Ticket is not valid, are the German ICE, IC/EC, and the Austrian RailJet (RJ). The Ticket is valid for regional trains in Bavaria, which include RE and RB of the Bahn and private trains, some running on the privatization policy of the Bahn, including ALX, Agilis, Meridian (Rosenheim to Munich, Kustein, and Salzburg), and Bayerische Oberlandbahn (BOB) operating south of Munich from Holzkirchen.

Thank you very much for the information. When I buy my tickets, should I ask what trains I can take or is it easy to figure out?

The train type is part of the train number. For Instance, standing inside Salzburg Hbf tomorrow morning and looking at the departure board, you might see
RJ 1164 to Munich 8:56 (this is not eligible)
M 79420 to Munich 9:15 (this is eligible)
EC 218 to Frankfurt via Munich 10:00 (this is not eligible)

There is also a printed broadsheet behind glass, (usually in yellow) with all the train departures for the entire day with notes showing which days of the week they operate. It will be in the main hall and on all the platforms. Trains designated M,RB,RE,IRE,S are eligible, trains designated RJ,ICE,IC,EC,CNL,EN are not eligible.

Raymond, you wrote: "When I buy my tickets, should I ask what trains I can take or is it easy to figure out?".
Yes, it is easy enough to figure out. You will (should) be getting your ticket from a ticket machine, to save the €2, so there won't actually be anybody to ask unless you go to the info counter..

The routes covered are shown in the map I posted earlier: https://www.bahn.de/p/view/mdb/pv/deutschland_erleben/allgemein/tickets/pdfs_laender-tickets/2015/mdb_190311_streckenkarte_bay_2015.pdf

On the departure board all the trains are listed with number, "ABC123" etc. Click here for a photo, you can see a 09:55 departure, train M79313 to Salzburg, platform 11) The letters indicate which type of trains they are. If you buy a Bayern Länder ticket you are not allowed to use IC, ICE, EC or RJ trains (it says so on the ticket). R, RX, S etc. are OK. If you buy a normal ticket, you can use any train, unless it is for a specific train.

I suggest you do some research and look up the times for trains from Munich to Salzburg on www.bahn.de

This is the webpage I use for looking up Bahn schedules. The link above will take you to this page eventually. Why not start here.

Even if you get your Bayern-Ticket from an automat, you can still go to the ticket counter and ask the clerk about regional trains leaving soon (or whatever time you want). In the past, they've printed out a schedule of trains for me. You can also print out schedules from the Bahn ticket automats. Finally, as Sam mentioned above, there are printed schedules posted throughout the Bahnhof and on all the platforms. The schedules on the white sheets are for arrivals; you don't need them. You're already there. The yellow ones, shown here, give the trains departing all day long and their destinations.

Thank you again. Very helpful.