I've never fished that area before, but would rule out a 5 weight anyhow simply because you would be ruling out too many flies from your arsenal due to wind resistance and too many days from your calendar due to the wind. On calm days you could use a 6 wt for smaller redfish and so on if caught on the flats or open water.
I don't know the size of snook in that area, but unless they are wide open beach fish, you would not be able to keep them away from pilings or mangroves with a 6 wt, and most flies used for them start at about 3" long.
The smallest rod I use in the Keys and for bass fishing is a 7 wt., but most of the fish I target run from 10 lbs to 50 or 60 lbs, with the exception of bass and tarpon on opposite ends of the scale. Although I "target" largemouth bass over 10 lbs., I haven't yet been successful.
I would check with your local fly shop and/or fly fishing club when you get there before making a decision.