Mike,
I have done a couple of Keys trips before ... and I just book a 4-day weekend trip in October with the wife ... I have to give her free riegn on a shopping run to Key West, but it gives me a full day on the flats ... Ft. Lauderdale is about 30 mile north of Miami, so it would add a half hour to the drive South ... but Miami and Ft. Lauderdale are both a heck of a lot cheaper and easier to fly into ... There are a few nice beaches that will offer a chance at bonefish along the drive .... There is a good book out there ... Flyfisher's Guide to the Florida Keys published by Wilderness Adventures Press ... The folks at The Saltwater Angler in Key West have been very helpful to me in the past - line choices, fly patterns, wading locations, etc. ... worth giving them a call as well ... February and March can be a little dicey depending upon the weather ... April is a decent month, fishing improves and the angling crowds have not yet decended upon the area ... Early May can be great ...