I guess I'm semi-retired. I've got a roughly 2-3 year plan to buy a boat and cruise around a while and see how the life suits me, then figure it out from there.
I know that area extremely well!!
First, if you are going to learn the boat there, you will not want anything over 6 foot draft with preference well under.
Good place to stay is probably Snook Bight. I kept my boat there for years, will be again soon if I don't head further south. THey are in the midst of replacing their docks, but be aware, it is still about a 6' approach around teh Mound House at mid+ tide. But there is a Publix right behind it in walking distance and the trolly runs pretty regularly. It is an easy walk to the beach too. Nice pool upstairs an a good restaurant too if you don't mind spending a few bucks (little more upscale).
FMB is very low key. Good restaurants are Nervous Nellies and SOB (Smoking Oyster Brewery), though it is often standing room only. The Hooters there is very good too - not your typical Hooters. Is a bit more of a locals hangout. Next to that is the cottage if you like some night life. Always a live band at night.
I really think FMB is a awesome place to get your skills down. The water is calm and there are a lot of destinations. Cabbage Key, Factory Bay (Naples), Keys, and when you are ready, the Tortugas cannot be missed.
You might also consider migrating south to Marathon. That is my favorite place in the keys for us (as a family). Key West is not for us except by day. Marathon Marina I think is the best place to stay unless you want to grab a ball in Boot Key. Lots of restaurants, etc. I can give you lots of info there too if you want.
Good luck with it all!!! This is where it gets exciting.