I would recommend flying into Ft Lauderdale versus Miami. To me it’s worth the extra 20 minute or so drive. It’s just a much more user friendly airport and the proximity to rental cars and the turnpike and 95 is simpler to me. I consider the Keys a true National Treasure every American should see at least once in their lifetime. They market it "The Florida Keys and Key West" for a reason. There’s the Keys, then there’s Key West. Culturally speaking, they are rather different. Key West is good bit more urban and touristy whereas the rest of the Keys have somewhat of a semi-rural feel to it. It’s all awesome though. On Key Largo I would recommend eating at Ballyhoo’s, that’s where the locals go a lot. In Tavernier on the south end of Key Largo the Sunrise Cafe will offer the best Cuban sandwich and cafe con leche you will find. For diving there I would recommend Conch Republic or Rainbow Reef for charters. For gear, SCUBA Outlet, ask for Warren there. I can’t help you in Marathon much, sorry. Looe Key Reef is a must and the operators out of Bahia Honda State Park are good to go in my opinion. I’m not a big fan of the diving out of Key West other than the wreck diving but others may offer better insight. I hope this helps. Have fun!