Yes you can take the major trains between these destinations :)

Yes you could but note that this upgrade is the difference of the standard fare 2nd class and standard fare 1st class on this route It can be quite high and if you think about 1st class i recommend to buy a 1st class railpass :)

Maybe change a bit your Route :)

Munich - Innsbruck (via the scenic Route over Garmisch Partenkirchen) then via Zell am See (few hours stopover) to Salzburg  then further to Vienna and finally one of 2 direct Railjets from Vienna to Venice :)

alternativ Pass option
If you wanna save money i can suggest the “German Railpass” as this pass covers the trains Munich - Salzburg
Salzburg - with a change in Rosenheim  to Innsbruck (sadly the direct ones are not covered by German Railpass)
and finally Innsbruck - Venice direct Eurocity

for the section Salzburg - Vienna - Salzburg i recommend the cheap railcompany called “Westbahn”

Thanks Seewulf.  Very helpful.  Unfortunately, Vienna needs to be the first stop due to business matters.

With your response, it’s apparent you have a very good knowledge of the travel opportunities in DACH.  I’m wrestling with a decision right now:  Do I stay in Salzburg for an extra day and depart for Venice from Salzburg or should I try to squeeze in one day in Innsbruck in order to got up to the Nordkette for the huge views of the Alps?  This will be our only chance to see the range during our trip.

Thoughts?  Thanks for taking a moment to reply

Salzburg is also nice but if you wanna see mountains, I would recommend you to go to Innsbruck. Nice Little City with many students and also a good connection to Venezia.

For mountains i prefer Innsbruck ofcourse there are mountains arround salzburg aswell and Famous villages like Berchtesgarden or Hallstadt but in my experience Innsbruck offer more :)