X2 on Crystal River and we use Birds of a Feather to go out and interact with the Manatees curious by our presence and especially the babies. Best interactions we've personally had were at very beginning of November, but they should be around still when you intend to go.
If you love beach, check out Boca Grande - Gasparilla Island = one side is where the tarpon are caught as the crab washes out from Charlotte harbour, and the other side is like being on a Caribbean Beach = stunningly beautiful. We enjoy exploring around the island and take a picnic for the day (private charges to cross the bridge onto the island and a small donation for the park). See lots of tortoise and iguanas here as well as many birds.
We have a house in Sarasota and we love exploring the man made as well as natural areas. Loved staying at Oscar Sherar SP and exploring (armadillos aplenty!), Turtle Beach, Venice Beach (sharks teeth), Englewood shelling. Myakka State Park we love to head to and Kayak and view all the gators sunbathing around us. Likewise further south Naples down to the Everglades and Miccosukee Indian reservation promity. Being on the water and exploring various inlets, mangroves etc is a wonderful way to experience the Gulf side right down into the keys. Take an airboat ride into the Everglades.
There's not much snorkelling opportunities until you get down to the keys and go offshore in a boat typically, but we'e enjoyed snorkelling around Point of Rocks Sarasota = just off Stickney Point and Midnight Pass Road (check a map!).
We are not ones for paid private parks, but one we highly recommend and donate to is NE of Sarasota = The Big Cat Habitat - it's a wonderful few hours for a fair entry price, run by the remaining Circus family the Roseiros.
Kayaking/Canoing around the canals, mangroves etc around Sarasota and all the way heading south on the gulf is a fabulous way to become at one. Google will be your friend here, and enroute there's some neat farmer/craft markets to experience.
Hope that helps. There's also a Casino enroute from Fort Myers towards the Everglades that allows free O/N camping, we like to stay at just before heading into the keys, if that appeals to mix things up a bit for a night.
Venice Pier = no fishing license required to fish off here we have been told in case any interest in that. Also you might enjoy experiencing the North and South Jetties (food is basic but we love going to POPs to sit and have a burger overlooking dolphins entertaining us, congregation of snook and various birds around). The Jetties is where most folks go to see the sunsets each night. There is a drumming event weekly at one of the beaches = think it might be Siesta Key (baby powder sand).
Hope some of these help you. On the Atlantic side, we love Fort Lauderdale over Miami moreso and enjoy working our way up to Palm Beach stopping at little places enroute.
Enjoy - now I wanna come with you!!! SD.