A couple of points about the Keys:
1. Someone above claimed that gas costs a lot more here.
They are completely wrong !
Here in Key Largo there are lots of stations, and a few of them are the exact same as those in Homestead and Florida City, while others might be a few cents a gallon more. I wouldn't wait until Key West though. That place is a tourist trap!
2. If you are looking for wide open beaches with a big distance between the water and the dunes like there is on the east and west coast of FL.
you won't find them on the entire length of the Keys. There are a few small ones like Sombrero Beach in Marathon, Bahia Honda SP and Mathers beach in Key West.
If you do plan on a trip to the Keys, post again here prior to your trip and those of us who live here year round or for six or seven months in the winter can supply you with more info (that doesn't come from those who have had just one or two trips to a specific Key or Key West)
Guy