Direct Train - Munich to Vienna

Jonsie if you know when you want to travel, you can buy advance tickets direct from the railway company and get discounts. Tickets for November are currently selling at €29.90

"Any specific rail carrier advice?". Most trains are run as a joint service run by DB (German Railways) and ÖBB (Austrian Railways).
There is a direct service every 2 hours; 09:30, 11:30 etc. There are also other trains where you change at Salzburg,
You can buy tickets on either site (DB or ÖBB). Tickets are "print-at-home". You just take your printout with you and show it on the train when the ticket inspector comes round.
There are also some competing trains run by "Westbahn". These use the same stations and tracks. These are listed on the DB site, but DB won't sell you tickets.

DB website: https://www.bahn.com/en/view/index.shtml
Enter from: Munich, to: Vienna, and a date and time. Click on "Search".
It will show all the trains, and you can buy tickets (but not for the Westbahn trains).

Luggage - makes no difference to pass or advance tickets, you sit in the same coach. As long as you realise you have to carry all your luggage yourself, hand luggage only. Read this webpage: https://www.seat61.com/luggage-on-european-trains.htm

The OEBB Railjet goes direct 5 times a day taking 4 hours. Reservations are not required. You can buy seat reservations for 4.50 EUR each at www.bahn.com. When you look up the day and itinerary, click on the small "seat reservation only" at the bottom of the "More options" page. Or just buy them when you get to Munich.

So if you go with a Eurail Pass, you just get on the train and show your pass when the conductor comes by, with the dates filled out.

Whether it is advisable to buy a Eurail Pass is a whole different question. I wouldn't.

Chris F and Sam, Thank you so much! I will review the information you've graciously provided. Many thanks!