I'll offer my thoughts, from America (though the Canadian end of the continent).
Though the people of the United States can be delightfully relaxed generally, I would suggest that you would like to be seen as being a person worthy of serious, professional attention. I would definately avoid wearing a T shirt and shorts - anywhere, while piloting a plane. Save that dress for when you own the plane.
Speaking of owning a plane... If you did, how seriously would you receive a pilot who turned up asking to fly it, without apperaing professional, organized and prepared?
Deloght in the apparently relaxed environment around the US FBO's, but don't be fooled, the fellow who just came back behind the counter from fuelling on the ramp, might own a half dozen of the aircraft out there. The young lady might be the Chief Flying Instructor.
I would want to appear professional and prepared all the time...
Enjoy the flying in Florida. Remind youself that it is a rather large area, and a lot of the south west half is not to be taken casually while over flying. It looks like you could set down lots of places, but swamp and aligators are abundant. The Keys are a very pretty flight, but few suitable forced landing areas.
I hope that helps,