As others have pointed out, this will be spring break time, so expect lots of kids (college and school age), lots of crowds, and pricey lodging.

Great suggestions on places to stay. B&Bs in Key West are preferred over traditional hotels, unless you plan on using points. There is a parking garage where you can put your car downtown Key West for long periods of time.
There are some great stops along the way down the keys on the way to Key West. Do a search here and you will find them.