bobthebob, I like your quantitative approach, and your calculations are solid!
However I don't no if your statement that "we need the same (molar) amount of NAC as acetaldehyde [and thus ehtanol]" is valid.
NAC seems not to be directly involved in the reaction of acetaldehyde to acetic acid (Acetyl-CoA), but is involved in the catalyzation by acetaldehyde dehydrogenase of the reaction:
CH3CHO + NAD+ + CoA → acetyl-CoA + NADH + H+
Wiki: "Cysteine-302 is one of three consecutive Cys residues and is crucial to the enzyme’s catalytic function"
i.e. the 1:1 molar ratio assumption might be incorrect, though it's unclear to me how much cysteine is "used up" and wether the mentioned cysteine replenishing will work (or is wise)
Looking forward to your (or anyone's) reactions, nice discussion!