From what I recall, Ft. Henry is kind of a tricky spot; to economize manpower on the cordon, you want a spot that's within easy marching distance of the Cumberland, above the railroad to Memphis, but below the Kentucky state border, which limits your options. Dispensing with KY neutrality altogether after Camp Dick Robinson opens would be an option, but potentially very risky.
I would like to think Lee would have done a better job defending TN than Johnston, as Johnston failed to ensure that his orders to fortify Nashville were obeyed, thus allowing the city to fall without a fight when Fort Donelson could no longer shield it. I've heard north TN is very defensible terrain, with concentric rings of hills, so if Lee plays his cards right, you could have a much protracted struggle over TN, which is good for keeping the US out of the Confederate interior.