Jan met us at the apartment as soon as we arrived, and gave us an overview of the area, including restaurant recommendations. He was very welcoming and quick to respond to questions. He told us that the Military History Museum was just a short walk away, which we hadn't realized before we arrived!
There is so much natural light in the apartment, and having two balconies was a dream. The water was hot, the thermostat worked well, and the neighborhood was quiet.
Stephansplatz was a healthy 25 minute walk from the apartment, with all kinds of shops and restaurants along the way. We took the S7 from Rennweg to Mitte, and transferred to the U4 to visit Schloss Schoenbrunn, which took maybe 30 minutes?* We actually didn't get a chance to walk through Belvederegarten - maybe next time!
*we usually depend on Google maps for public transportation directions; however, it seems to be incomplete for Vienna. We recommend looking at a public transportation map instead of Google maps if you want to use the trains.