I used to live in DC and now live in Miami. You could easily spend five days here.
If you stay at a nice hotel on South Beach, it won't be too noisy. However, driving on SB is kind of a pain. Which hotel are wedding guests staying at -- I'm guessing it's in Coral Gables? My inclination would be to stay there and drive over to SB for a day.
In terms of restaurants, there are tons of good places. Let me know a little more about what you like to eat, what price range, etc. In general, I think Eater has good recommendations:
http://miami.eater.com/maps/the-38-essential-miami-restaurants-july-2014
I second the recommendations for Vizcaya and Shark Valley/Everglades (*definitely* take the tram tour!).
You will want a rental car. Public transportation in Miami is pretty bad. If you stay on SB, you won't need a car, except to visit some of the attractions.
I love being on the water, so I recommend a boat tour. A walking tour of Little Havana would be fun and unusual.
Frommers has a pretty good attraction list:
http://www.frommers.com/destinations/miami/attractions#sthash.gSg0IeuX.hOdGXYQi.dpbs