On just a couple of points.
I have and continue to use red rosin paper under wood floors for (2) reasons. 1) to prevent dust from filtering up fron the subfloor. 2) to help prevent squeeking/creaking of the two layers against each other. Also, for the low cost, what can it hurt?
If this is full thickness 3/4 inch harwood flooring, 1/2 inch plywood subfloor is fine as long as your laying the hardwood floor perpendicular to the floor joists. I am assuming the joist are on 16 inch centers. In the "old days" many hardwood floors were laid directly over the joists with no subfloor.
Just My 2 cents.