If you are serious about visiting of the sites like Pompeii, Amalfi,, Heraculaneum.. then the cooler Spring will make this a far more comfortable experience. Accommodation with a pool may be a consideration for some.
Sorrento itself has limited beach areas and they can get very busy in July and August. Fortunately to get to Pompeii, Herculaneum and, if you wish, Naples you can use the excellent Circumvesuviana train service. The traffic in this direction from Sorrento can be chaotic and makes driving slow. Likewise the ferries, hydrofoils and "Metro Del Mare" operate services from the beginning or end of April until the beginning or end of October
