You should have no problem with the language, as my wife didn't speak a word, and had no trouble. And, every time, it seemed, I tried to speak to them in German--remembering it from some 30 years ago, they always responded back in English.

But, in addition to learning the basic phrases, you really have to learn the names of all their coffees if you plan to hit any of them. Even though they know what a cappuccino is, you have to call it, IIRC, an einspaenner. Even "mit schlag" didn't seem to work for me--they wouldn't let me describe it, I had to name it. But, coffeehouses are a big tradition in Viennna and they hold to a certain decorum. We enjoyed it, as I'm sure you will.

And, I do second taking the S-bahn. If memory serves, it was 3 Euros vs 9, even though it takes 29 minutes vs 16, back in December.