Jean, Best Wishes on your upcoming wedding! Siesta Key is a beautiful location for weddings.
On our website (www.ElegantSarasotaWeddings.com) are listed various Accommodations, Reception Locations, and Reception Locations Waterfront. That is a very good place to start — you can see photos of their sites.
You can get married on one of “their” beaches or on the Siesta Key public beaches (check with Sarasota County Parks & Recreation Dept. about getting a permit).
Best of luck,