Sorry Jay, I misunderstood. Now I see that you never proposed to go to Pompeii.
I often point out here that some people prefer Ercolano because they imagine that it was so much easier to "see it all." But in fact, most of the city is forever buried under the modern city of Herculaneum. Likewise, our host here, Rick Steves has pointed out that Pompeii must have had a Synagogue. But it has not, so far, been found. Plenty of Pompeii is still out of sight.
Anyway, two places are easy to do in a day. Ercolano, unlike Pompeii, has only snack vending machines inside the site. And you cannot exit and reenter. Eat as early as you can to preserve as much time as possible for the excavation. Some villas always turn out to be closed for repair or for a shortage of guards. Winter hours are shorter due to dusk time.
AFAIK, all the Farnese Marbles are in Naples. Actually the sculptures in the Borghese Gallery are better, but the Farnese Marbles are pretty famous.
The line to buy Arte cards in the Naples station was impossible in May so we gave up and did without. Maybe you won't end up behind people from three different countries, who had a host of questions for the schmo behind the counter.