To rent a boat in Florida, you need to complete an approved Boating Safety Course. The FWC website links to approved courses for this. If you were born before January 1, 1988 you are exempt from needing this certificate.
What is required to rent a boat? You need to be at least 27 years old of age & have a valid photo ID and a major credit card. Also if you were born after January 1st 1988 you need to have the Florida Boater's Education Card or equivalent in another state or country with you.
No, you are no required to hire a captain if the vessel is registered as a pleasure craft. That said after about 40 feet you will most Likely need crew to safely run it.
Florida boaters must have a license to operate motorized watercraft. However, you're more likely to see it called a Boating Safety Education Identification Card. It's a requirement for boat operators born on or after January 1, 1988.