Ferry leaves from Battery Park; allow 3–4 hours total (including security); ferries typically run from ~8:30am to late afternoon — check seasonal times.
If schedule allows, a short window to see Liberty Bell exterior and grab a lunch bite at Reading Terminal Market (open most holidays but check Christmas hours).
Reserve a week-long minivan (Chrysler Pacifica / Toyota Sienna class) sized for 7 with confirmed insurance and a GPS/Wi-Fi option; pickup near the airport or downtown depending on your lodging.
Choose a safe, central neighborhood — South Beach for nightlife/beach, Brickell for transit and dining; get a parking pass or a hotel with on-site parking for the minivan.
Book a group-friendly dinner in advance or join a public fireworks area (Bayfront Park or South Beach) — expect crowds and earlier road closures; check local NYE event times.
Key West is ~160–170 miles (4+ hours one way) and makes for a long day — consider an overnight if you choose it; alternative: extra time in Everglades or Biscayne National Park day tour.
If driving all the way back to Southfield, consider breaking it into two long days; flying back individually from Miami is faster and often economical for students.