You don't really need a tour guide unless you just want one. I've been to Italy numerous times and never had a problem getting around. People are quite friendly and wish to be helpful.
Capri is a wonderful place to visit, especially if you can spend at least one night there. The tour boats leave in the late afternoon and then you have the island to yourself and the natives. It's a very magical experience.
We used Sorrento as a base. It's on the Bay of Naples and an easy drive from Rome. From there you can ferry to Capri and Naples (I strongly suggest not staying in Naples, but instead just doing a day trip there). You can also drive to Pompeii, Positano, Amalfi, Herculeneum, and Paestum (a very underrated Greek ruins site) for easy day trips to minimize the number of times you have to change hotels.
I would volunteer to accompany you as tour guide, but my wife would undoubtedly object.