Hi Tony,
Pompeii is very easy to reach on the local train. You want to get off the ship as early as you can to beat the tour buses. My husband and I each purchased a headset. I can't remember the price but it was reasonable..like 9 euros for two. Tons of tourguides there if that is what you want. We saw some of the ship tours and thought they looked crowded.
Now if I had to do it again...I would skip Pompeii and go to Herculaneum (Not sure of the spelling..I think it is called Urculana in Naples) instead. I believe it is a stop or two before Pompeii on the train. The seasoned travellers I talked to said that although it is smaller, it is better preserved and less crowded. Although I loved Pompeii, I still wish I had gone there.
As for your alchohol question....I bought a couple of bottles of wine in Rome and put them in my checked luggage. I don't know what they would do if you have wine or liquor in your carry-on. When I was ready to bring wine to the dining room, I would leave a bottle out and the steward would put it on ice in my absence. The corkage fee was twelve dollars and is cost effective, even for a cheap bottle of wine. I don't foresee any problems enjoying drinks in your room. Hope this helps.
Doreen