Darling,
This answer will come too late for your soiree in South Beach, but having a property down there, I know exactly what Miami Chic entails: dressing like a whore, but making a point of not charging like one. I know, sad right? South Beach has a vibe and fashion sense of its own. Miami Chic means lots of flowing skimpy fabrics, high heels, big hair. Colors, colors, colors. Versace, Versace, Versace. Pick any of Paris Hilton's looks and you will fit right in.
Oh my God, I just realized you are a male! All the above goes for you as well... But if you want to tone it down a little, then white suit and black shirt, black shoes will look very Miami and very chic.