Train between Vienna and Salzburg & between Salzburg and Munich

I think you need reservations for these routes, the popular cities are either required or recommended. If you know your dates, I'd do it as soon as possible - they do book up. Try the raileurope website or deutschbahn website, it'll give you travel times and prices. But if you want fast, look for direct trains and high speed lines.

Reservations are not necessary. You can actually take a seat on the Westbahn train and pay the conductor for the ticket. They go hourly and are as fast as the Railjet trains.
Salzburg to Munich can be done on a local train with a Bayern ticket without reservations. It is not as fast as the EC or Railjet trains, but the cities are not far apart. And with a Bayern ticket, you arrive able to use Munich's transport (S-bahns, U-bahns, trams, buses) until 3 am the next morning.
https://westbahn.at/en
https://www.bahn.com/i/view/GBR/en/prices/germany-regional/bavariaticket.shtml

Wanderkins - a big no to Rail Europe for fares and schedules. Also, please note that reservations are totally not necessary on these routes.

Getting from Vienna to Salzburg you have two options - 1) private Westbahn trains from Westbahnhof; fares are 25.50 Euro per person and you buy the tickets on the train; trains leave every hour; they have free wifi; 2) OeBB trains for 19 Euro bought in advance, online; trains leave from Hauptbahnhof or Wien Meidling. Travel time differences between these two options is negligible.

From Salzburg to Munich, the Bayern ticket, described above, is the way to go. Here's the link - https://www.bahn.de/p_en/view/offers/national/regional/laender-tickets/bavaria-ticket.shtml

There are basically three trains between Salzburg and Munich.

The high speed Austrian train, the RailJet, or RJ, makes the trip in about 1hr30min. It makes no stops between Salzburg and Munich Hbf.

The EuroCity (EC) train take 10 minutes longer, because it makes a few stops, including Munich East (München Ost) Bahnhof, from which you can catch the S-Bahn to stops in town , like Isartor and Marienplatz, or to the airport.

The regional Meridian (M) train take another 10 minutes (1h51m) because it make more stops, including Ost, but it is usually less expensive because you can use the Bayern-Ticket on it.

None of these train require a reservation, although they are optional on the RJ and EC. There are no reservations required or available for the Meridian train.

If you purchase tickets at the time of travel, the RailJet will cost 36€, the EC 32€. With advance purchase, either the RJ or EC can be as low as 19€ for a non-refundable SparPreis ticket.

If you use the Meridian, you have two choices. The Bayern-Ticket, for 23€ single, will cover you from Salzburg to Munich and allow you to use any conveyances S-/U-Bahn, trams, or buses) of the MVV (Munich metro) that day. A Guten Tag Ticket, for 21€, will cover just the Meridian train to Munich. Either ticket is available up to travel time for the same price.

Note: the fully flexible ticket for the EC is 32€ ($36) from the Bahn, $45 on RailEurope. For the RailJet, it's 36€ ($40.50) from the Bahn, $52 from RailEurope. For the Meridian, it's 23€ ($25.86) for the Bayern-Ticket from the Bahn, 30.70€ ($34,55) for a full fare ticket, $45 for a full fare ticket from RailEurope (they don't sell the Bayern-Ticket).

Advance purchase tickets for the RJ or EC are as low as 19€ ($21.37) from the Bahn, $31 from RailEurope.

Wow. Those RailEurope mark-ups are stiff.

Those RailEurope mark-ups are stiff.

They've got to make a profit somehow. That's why the consistent advice on this site is not to use RailEurope if you can avoid it. They're more convenient, but you pay for the convenience. Note also that there is likely to be shipping and handling (min $18 on the whole order) on top of the ticket prices from RailEurope.

In most cases, refund or exchange would be easier to do with a ticket from the Bahn vs from RailEurope, and you'd get more of your money back. The one exception is the Bayern-Ticket. Bayern-Tickets are non-refundable. The full fare tickets from RailEurope (or the Bahn) and refundable and exchangeable, although RailEurope charges more to do this.