Flying up
Nonstops to Atlanta leave from both MIA and FLL, about two hours in the air.
From MIA, the MIA Mover links the terminal to the Miami Intermodal Center, where Metrorail's Orange Line and Tri-Rail stop. If you live near a Metrorail station, you never touch the parking garage.
From FLL, Tri-Rail and Brightline both run shuttle buses from their stations to the lower level of the terminals.
On the Atlanta end, land at the Domestic Terminal and downtown is a short MARTA ride. No rental car needed.
Driving is about 660 miles, a full day on I-75 and the Florida Turnpike. Fly.
March in Atlanta
Miami in March sits near 80 by day and the mid 60s at night. Atlanta in March runs highs in the mid 60s and nights in the mid 40s. Pack real layers and a rain shell. Spring allergies? The Atlanta page has the pollen note.
Calle Ocho falls on a Sunday in March, so check the Atlanta dates against it before you book. If May suits you better, Washington, D.C. is milder still: highs in the mid 70s, lows near 60.