Since you don't really drink i would say to skip Key West, its mostly bars and touristy shit. Other keys have WAY better beaches and provide awesome wildlife experiences.
Go here for key lime pie:
Bob Roth's New River Groves
5660 Griffin Road
Davie, Florida 33314
(954) 581-8630
newrivergroves.com
Go here for a lobster roll:
15th Street Fisheries
1900 Southeast 15th Street
Fort Lauderdale, Florida 33316
(954) 763-2777
gofisheries.com
If you go to South Beach, go here for Crab:
Joe's Stone Crabmore info
11 Washington Avenue
Miami Beach, Florida 33139
(305) 673-0365
joesstonecrab.com
Definitely recommend Las Olas for the night life if you want to party.