Hi Kristoff,
With its small streets and numerous BARS Key West is best explored on foot
Some of my friends stayed here last month.right in the old town.
http://www.spanishgardensmotel.com/ Be sure to catch the sunset from Mallory pier lots of street preformers make the wait entertaining
The speed limit from Key Largo is 45mph (70kmh) most of the way so allow lots of time.
The Everglades NP is a good day out from Florida City (Homestead) Stop at the visitor centre for the short film/presentation about the Everglades makes the visit more interesting.
South Beach is an easy visit but the hotels are expensive and Spring Break may mean they are all booked anyway. The ArtDeco area is quite small as i am sure you will want a picture or two
Hollywood Beach near Fort Lauderdale is worth a visit if you like to enjoy a cool beer and watch the girls go by on the boardwalk(concrete path)
Looking forward to seeing you in Sebring.
Phil