Pretty darned hot in Key West is about 90-degrees, but keep in mind that most of the time the humidity is relatively low. I've been there in June and July and the hottest days were in the mid 80s--I loved it! I've always found it interesting when folks from Maryland talk about how hot and humid Florida is, when most of them have never been there in mid summer. In Baltimore, mid August usually brings temperatures from the upper 90s to low 100s, with equal humidity numbers. I've never encountered those conditions along Florida's east coast, and especially in the lower keys. And, when winter arrives here, which is just 5 months after spring arrives, everyone is scrambling to put the boat on the hard and have it winterized. There ain't no winter in Key West!
Stock Island is a lot less expensive, and if you're willing to do some on-site searching you can sometimes find a private dock for a lot less. You just have to be ready to do some extensive legwork, but they can be found.
There's some great locations where you can anchor up safely, and if you don't have a high demand for electricity or water, these locations are quite secluded, and safe from most weather conditions shy of a full blown hurricane. Mule Key Basin is just west of Key West on the west side of the Northwest Channel. Been there several times, fairly deep water, and completely surrounded by flats. Even in a 30 knot breeze the water is pretty flat.
Getting in and out of Garrison Bight may be a stretch. Some pretty tight turns, plus a couple bridges, and during peak tidal flows the current between the bridge pilings can be treacherous. Flemming Key Bridge only has a vertical clearance of 18 feet and a very narrow opening. During a hard, outgoing tide the water resembles a waterfall beneath the bridge.
There is a deepwater channel around Flemming Key that will get you into Garrison Bight, but I don't remember if the Palm Avenue Bridge is a draw bridge or not. If my memory serves me correctly, this was a fixed bridge the last time I was there.
As for hurricanes, Key West tends to be one of those locations that is often skirted. If you look back through the hurricane archives you'll find some solid information on this. Keep in mind, however, that if one does hit Key West, there's really no great hurricane hole to duck into other than Garrison Bight, and it will be jammed solid with other boats if there's a bad one on the way.
Good Luck, and I envy your retirement plans.