Grüss Gott, Katie.
I’m not a native German speaker, but it seems to me you should learn standard German first. All Austrians use exclusively standard German in school — plus you can use it in other countries, including Germany, which has a population on the order of ten times that of Austria. I doubt there are any good resources for learning Austrian German from English; normally it’s expected you already know standard German. Once you’ve learned some German, and you’re sure you’re going to Austria, you can find some resources on line to study in-flight. Once you’ve landed in Vienna, you can pop into any bookstore and find material written in Austrian, Wienerisch, Bairisch, etc. (Note that most Austrian German is classed as part of Bavarian, except for the Vorarlberg which is more akin to Swiss German. Wikipedia has a version in Bavarian, if you’d like to familiarize yourself with that variant.)
That being said, you should immediately learn the phrase I opened this comment with, since you’ll likely hear it as soon as you get to customs and immigration. and you don’t want to get discombobulated before you’ve even had your passport stamped ;)
There’s an italki teacher from Austria who has been very active on the forum lately, I’d send him a message if I were you (you could also do a teacher search for German teachers from Austria):