If you are determined to use a fly rig, crab and shrimp fly patterns will catch pretty much anything from reds to snook. I prefer yellow/white or white/brown colors, although bright pink shrimp imitations work well too.
I'd use a 6wt with a 6lb tippet, but whatever you feel the most comfortable with. I fish mangroves on the flats for reds, never had a problem bringing them to the boat. Might be different in Florida, but here a 2 lb snook is it, the reds are actually larger.