Pub,
If you want an actual beach then as Rick stated, go to Bahia Honda State Park. Park in the lot furthest to the east or left. (all beached in the keys face south) Then walk as far as you can to the left. Don't ride in front of the boardwalk. Plenty of room to set up and launch. The fee is only a couple of bucks and Bahia Honda was named 1 of the top 10 beaches in the US. Smathers Beach is another spot that is in Key West or check with the Kitehouse for a ride to the flats. Islamorada is pretty much the mecca for kiting in the keys. While passing thru, stop in and say hi at The Otherside Boardsports and/or Seven Sports in Islamorada.
Have fun and stay safe!!
Noel
www.othersideboardsports.com