It is an epic adventure alright. I have cycled to some of the places you have been. The southernmost point in the contiguous US is in Key West. Traffic on the islands on coastal florida is much easier to handle than on US 1. Miami can be traffic dense. You should be ok. There is plenty of dedicated bike path running beneath the metrorail track along your route to the Keys. You might want to take Card Sound Road instead of US 1 going to Key Largo. It is known to be safer. However, the last time I cycled US 1 to the Keys there was a lot of new road construction going on, so maybe the situation has changed by now. Try not to cycle the bike path beneath metrorail after dark just for the sake of safety. As you come to where US1 starts going to the Keys you will find the Last Chance Saloon. If it is open you can have a beer. There are places in the tall grass far in back of the place to lay it down for an evening of stealth camping. I cannot totally vouch for the safety of the place, but I have used it three times, and I know another fellow who stayed there a few times when cycling. We had no problems whatsoever. Palm Beach Island is a good ride. Stop in at Worth Avenue and see how the rich people do it. See how many chauffeur-driven Rolls Royces you can see in half an hour. I counted about fifteen. You can also take Jupiter Island where some of America's oldest and wealthiest families spend their winters, and other seasons. The place has changed somewhat over the years.
Take Bridge Road in Hobe Sound to Jupiter Island. Go south. You will have to get on US 1 to go around Singer Island and Palm Beach Inlet. Get back on the Island road to Fort Lauderdale. Go around that inlet and get back on the island to Miami. Once you are in downtown Miami go to the Dupont Plaza building, south across the Miami River, and and along Brickel Avenue which will reconnect you with US 1 which you will not have to get on for quite a distance because of the dedicated bike path under the metrorail tracks.
Just a few suggestions, not that you are expected to follow them. In my opinion, You are much less likely to encounter problems on the island route than you are taking US 1 and routes farther west. It is not guaranteed, but I am a native of that area, and I know where to go and where to avoid. I do guarantee you there are places you do want to avoid not far off of US 1. Not that I want to badmouth anywhere, but the fact is there are quite a few high crime areas and drug dens and places where drive-by shootings seemed to be taking on the aspect of a national sport, and those places are on the mainland and not far off US 1.
