Scottsville, VA, on the James
Hello again friend,
Driving from the southern end of the Skyline Drive at I-64, to Scottsville, and then along VA 56 back to the mountains is, quite frankly, a terrible idea. The ride back towards Lexington is particularly lousy with curves. You're liable to have a car full of carsick people who'll be seriously mad at you if you do this.
Far, far better to jump on I-81, a nice drive in and of itself, and run down to Buchanan if tubing the James is a must.
As to Day 3, the NC State Zoo is just outside of Asheboro, just south of Greensboro, along the US 220/I-73/I-74 corridor, and is a large "natural habitat" zoo with very few bars/fences to be found. Perhaps another 2.5 to 3.0 hours to North Myrtle from there?
Foy