Definitely rent a car. A rag top too. The most expensive variety you can afford.
I usually get a ‘stang for my winter jaunts. Barring that Hertz has Panamera’s at MIA. It is just starting to be convertible weather again. SOBE is wall-to-wall nouveau riche socialites or wannabes with a gaggle of tourists throw in. Expensive, packed. It’s worth a look but unless you love crowds it is not a place to stay for long.
Dinner tips: For beef - Red the Steakhouse & skip the over-hyped Prime One Twelve. BLT is also very good. Old Lisbon is good in Coral Gables for earthy Portuguese food & awesome fish. Big Pink is a standard for funky lunch in SOBE. For sand: Go to South Miami Beach to see or be seen & Haulover Beach in Sunny Isles to REALLY be seen.
Ian