contact Brad Lang at 7 Kiteboarding at Whale Harbor (Islamorada) for suggestions on hotels....or (probabloy just as easy) search it on the internet.
I've stayed at the Keys Lantern (I think that was the name)...decent rooms, some with kitchenettes. If you call them and they don't have space they will tell you of other hotels.
A word of advice...weekend rooms fill up fast. Make reservations. Nothing is cheap in the keys...maybe with the current economy there are deals, but don't be surprised to pay $100+/night minimum.
From Islamorada you can hit Whale Harbor, Anne's BEach, Bahia Honda SP without boat support. If the wind is out of the NW, N, NE you can get Brad's outfit or Other Side to give you a ride to the back country.
Key West is a bit of a haul, and other than Smathers beach you will need a boat. So nothing terribly different (for riding exp) in Key West than in Islamorada - except if you need the Duval Street experience.
ALSO - If the wind is good in Miami, check out Stiltsville (need boat or water taxi) contact Miami Kiteboarding (Cristof), or head up to Delray, Jupiter
Depending on wind direction you should not rule out the Gulf beaches - Marco Island, Naples, Venice, Sanibel, Sarasota, Tampa Bay (my base of operation).
If you need more info feel free to contact me.
have a great trip and good winds