Key Largo is the best place for snorkeling

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.