You will need to purchase a new ticket once you are through visiting Pompeii to continue on the Circumvesuviana train to Sorrento.

There Pompeii Scavi station does not have luggage storage but the ruins at Pompeii does. There are audio guides available for rent and guides offering their services at the entrance to the ruins. You can usually find a couple other people to share the expense of a guide. Prices are flexible.