Key largo is only half an hour from the everglades east entrance, hightly recommend to go there for snorkeling. The John Pennekamp Coral Reef State Park has a lot of boat tours too.
Everglades is a must, try go to all three entrances. Remember to bring a binocular for bird watching. If you do go to the west entrance at evergaldes city, you may want to got to the chokoloskee island and hire a fishing charter boat. You can fish, and possibly see dolphin and manatee and a lots of bird. April is the month there are a lot of baby birds there.
In the nearby Big Cypress National Preserve, there are a lot of ranger led activities. You should check it out.
