Zojoe:
I used to live on Sanibel, but didn't sail then, so I can't recommend particular spots. Probably has much to do with where you can launch; from there, it all ought to be pretty good.
Prevailing wind in summer is from the southeast until the land heats up and the westerly sea breeze kicks in. The early winds are generally very light; the sea breeze can be 10-15.
Kevin