Thanks to all for the feedback, especially regarding the rate for the tour guide. If 200 euro is reasonable and in line with that most others are paying, then that works for me.
We will take Trenitalia from Roma Termini to Napoli Centrale and then the plan is to transfer to the Circumvesiviana line for the final leg. It sounds like that line is pretty terrible, but if our lives are not in danger, then I would take the convenience of being right at the entry gates to Pompeii on arrival. My rough Google map search shows an approx 30 min walk from the other Pompeii station, and although we are fine with a lot of walking, I would prefer not to add that to the overall travel time for this specific day trip.
I mentioned in an earlier post, but my tentative plan would be to book train tickets departing Roma Termini around 7am mid week. This would put us at the gates to Pompeii around 915am after the walk to and transfer to the Circumvesuviana train in Naples.
Figure 2 hours with the guide from about 930-1130, then we will give ourselves at least another hour to wander on our own.
We would like to get back to Naples in order to have enough time to eat at Pizzeria Trianon which is one of the 2 that Rick recommends, and which looks very good based on google photos and reviews. It closes at 330pm, so we need to ensure we get there in time to account for any waiting in line and eating. Thus I am thinking of a 1pm or 130pm latest train back to Naples from Pompeii.
After pizza we would head back to Rome, relax in our AirBnb and look for dinner somewhere and have a passeggiata.