Getting from Munich airport to Munich Hauptbahnhof

Just take the train -- cheap and easy.

The S-Bahn goes every 10 minutes (actually on a 7&13 minute interval) by 2 different routes, both of which call at Munich Hbf. A single ticket is 13.60 EUR, or you can buy a group ticket for 2 to 5 people for 23.40 EUR.

we will be arriving at the Munich airport, then taking a train to
Vienna from Munich Hauptbahnhof

I see three options from the Munich airport to Vienna. Only on option goes through the Munich Hbf.

First, and possibly the least expensive is to buy a Bayern-Ticket at the airport. That will cover your travel to Salzburg. Take the S8 (S-Bahn) to Ostbahnhof and from there board a regional BRB train to Salzburg. From Salzburg, take another train (probably the Westbahn) to Vienna.

Or, there is now a regional train leaving from the airport station. It goes to Regensburg. From Regensburg, you can take an ICE to Vienna via Passau.

Lastly, take either S-Bahn (S1 or S8, whichever is leaving next, to the Munich Hbf). From the Hbf, there are multiple options to Vienna, ICE, RailJet, or EC/BRB to Salzburg - change to Westbahn or RailJet to Vienna

The S1 or S8 from the airport will get you to the HBH, the S8 is the faster of the two. You can buy your ticket at the information desk. Tell the agent how many are in your party as it is cheaper than buying a single ticket for everybody, and that you going to the Haupbahnhof station. Be sure to sign your ticket before boarding. You may be asked to present this ticket, so be sure to keep where you can easily have it. There is a 40 euro fine if you are caught without a ticket (for each of you). Once there, follow the signs to the main train station. Do you have your train ticket to Vienna or will you need to buy it in Munich? If not, give yourself some time as the ticket master can be quite busy.
Have fun, too bad you're not spending any time in Munich. Great city!

Steve

While the S8 is faster, take the first one available when you get to the platform. If the S1 is available, take that one as it will get you to Hbf sooner than waiting for the S8.

I bought tickets for a "bullet train" from Rail Ninja for the trip from Munich to Vienna. Supposedly a little more than four trip. Bought first class tickets and plan on dozing on the train.

The tickets won't be available until June as this is a December event. Never used Rail Ninja. I know it is not the train company, but a broker. Hope they are reliable.

Supposedly a little more than four [hour] trip

The RailJet and WestBahn each make the trip from the Hbf to Vienna in just over 4 hours. With the trip from the airport to the Hbf included it is close to five hours, so I assume you only got a ticket from the Hbf to Vienna. So don't forget, you will still need tickets from the airport to the Hbf. Buy them at the airport. S1 or S8, same price, one ticket good for either S-Bahn. Take whichever one is leaving next (they leave from tracks on opposite sides of the single platform).

I hope your tickets from the Hbf to Vienna are "open" tickets, valid any time that day, since you can't predict when a trans-Atlantic flight will actually arrive.

You are absolutely overthinking it.

Just get off the plane, clear customs & immigration and head to the attached train station. Buy a ticket from one of the machines and ride into the city.

You folks are the bomb, Thanks!!