Wananewboat -
The place that I keep my boat is www.cedarbaymarina.com
They do rentals too...excellent service and nice people.
As to where to go by water, where do you start:
Stans in Goodland on a sunday afternoon.
Tin City in Naples any time
Head south into the 10000 Islands
Head north to Naples and Ft.Myers
There are a ton of places to go by boat.

The Marriott is a nice hotel...usually packed during season

All the best,