Meet up in Vienna

I'm so excited that people are excited to meet!!  I'm thinking Sunday, May 9th, from, say, 2:00 - 4:00 (I know people have work during the week).  Picking a location is the difficult part, as I've never been to Vienna!  I've gotten lots of recommendations for cafe's, restaurants, etc., but I'm not yet sure where exactly any of them are in the city.  Does anyone have a recommendation for a place that is centrally-located, easy to find?

Can't wait!!