Vienna, like Prague and Budapest, is a profound experience. Many commentators will describe the beauty of its baroque architecture, and endless other qualities. While these descriptions are often very accurate, one of its stand-out qualities is its people. I have been to Vienna several times and will be returning very soon because of the Viennese culture. My experience has been that the Viennese are, while relatively wealthy, particularly friendly. The Viennese are both gentile and sophisticated. I can only urge anyone who is travelling to Europe for the first time to start your European experience in Vienna.
It would not be possible to properly explore Vienna under 4 nights or 5 days. Must see in Vienna; walk and walk the entire 1st District. This includes Hofburg Palace and St. Stephen's Cathedral. Also The Abertina, Belvedere and Schonbrunn palaces, and definitely a performance at Motzarthaus.
Best time to go to Vienna. Anytime, but I love Vienna in the snow, but Spring is breathless, particularly Belvedere and Schonbrunn.
Last, please learn some basic German, even it's to say please or thankyou!