Since this is my sailing area, I would agree with all that is said. Starting out on the Miami area is a good start as well as Key West if you want to drive another 4-5 hours. Launch out of Coconut Grove Marine Ramp in the Miami area. Key Biscayne Bay is nothing more than a large swimming pool and a good introduction to sailing in the keys. I would use the ICW down to
Islamorada. Reason is not much to see on the ocean side down to this point and not many places to tuck into. Head down to Elliot Key for the first overnight. Anchoring in the keys. Most of the bottom is hard limestone with about 2 inches of soft sand or muck. Not good holding. I use a Danforth/Fortress anchor tied to my Ronca trip line hole with 8 feet of chain in series. This is the best set-up for the keys. Drop the Danforth/Fortress first, easy the boat back a bit than release your primary anchor. I have never dragged with this combination.
The ICW down to Islamorada is a pretty sail however it is very shallow. I have a 5' keel and constant attention and good navigation is a must. Staying in the channel most of the way down is the only way to make this journey. If your draft is less than 4' you will have a few more options than I do. The only other caution on both the west and east side of the islands is all the lobster/crap traps. The trappers have no ethics down here and mine the channels; ICW and Hawk Channel. So a careful look out is a must.
Once down to Islamorada and the weather is nice, I would go out to Hawk channel down to Key West. Great places to gunkhole, snorkel and dive. Also the fishing is good here too. At a somewhat leisure pace, it would take 4-5 days to get to Key West on this route.
You if care to read about one of my trips to Islamorada here is my log:
Rickenbacker Marina to Elliot Key | The Revolution