I did Miami to Key West to Jupiter with friends a couple years ago, in January. Southbound on the keys was glorious with a huge tailwind, northbound was ferocious into the same headwind. The Seven Mile Bridge going north was pretty horrid, crawling along beside heavy traffic. I'd suggest considering a southbound trip ending in Key West. An option: two of our group took a bus back up to Homestead, with bikes, for next to nothing while the others slogged against the wind all day.

King Seafood Market and Restaurant on Marathon Key was pretty fantastic.

I rode trails where they were obvious and not flooded or washed out - maybe 1/3 of the keys.

I think Miami to Key West, a day or two in Key West, bus back to Homestead, the ride back to Miami would be a great trip.