Dunno that a single speed is a good idea in hilly KY. And it's really not a good idea if you carry a lot. So I'd probably pick up an internal gear hub. A fancy one with 7 or 8 speeds will make most hills doable, but the really nasty ones will still be tough. (really nasty is 15% grade or worse in my book) Even a Sturmey Archer 3 speed hub will take some of the edge off.

If you'd rather have a derailler if you're doing gears, I'd go with mountain cranks. Sure, you might use a 52 tooth ring going downhill, but I'm chicken and would rather not try to hit 50mph on an Appalachian road. Too many blind curves. A 50 or 48 tooth big ring should be plenty big.

If this is a second bike, do whatever the hell you want .