How exciting, Janet! I was in Vienna in June and it was beautiful . . . and hot and no AC, but still beautiful. The tram and metro systems are good, both to get to places that aren't right in the heart of the old town and to save your feet in the old town. They are extensive and the maps are confusing but they are easy to use once you figure out which line to take.
I enjoyed Rick's audio guides and walking tours - especially the lunch stops.
I was disappointed with the flea market. There was little variety and a lot of goods imported from India (I think). It was worth a short walk-through.
If you like opera, get the schedule and then sit outside the beautiful building and watch the live performances on the huge screen. If you get there early enough, there are some seats. Otherwise, you sit on the sidewalk or stand.
Visit the Schonbrunn Palace and its gardens, skip the Hofburg Palace. The imperial rooms are nearly identical to those at the Schonbrunn (surprise, the same people lived in both) but there are more rooms to view at the Schonbrunn.
I had planned a day trip to Melk, but it was so hot, I decided not to overtax myself. There was plenty to see and do in Vienna itself.
Try your German, but don't be surprised or disappointed if everyone answers you in English.