Congrats on your 30th Anniversary this summer! We have our 21st this summer! Italy will be hot and busy with tourists in August. Spring or fall may be better? Italy has so much! How much time do you have there?
Central Italy...I suggest 5 days if you go to Rome. I really liked Rome and the Vatican City together because there was so much to see...the colosseum at day and lit up at night, the Roman Forum, the Trevi Fountain lit up at night, the Vatican and St. Peter's Bascilica are all must sees, plus much more!
Northern Italy... Northeast...Venice is a must see, but maybe just 2 days. You take a train and then a little vapretto boat to St. Mark's Square, take a gondola ride and hear about the history from your gondolier! We bought the most amazing canal painting from an artist for $100. Pompeii ruins are nearby.
Northwest...Cinque Terre was fun. They are 5 villages along the coast that you can hike or ferry between. Verrazana is the best village to stay. Bring a swimsuit for swimming among the rocks. There is a Lover's Walk between Monterosso and I think Vernazza. The villages are slow paced.
We went to Tuscany for a week with family and rented a villa to enjoy company by the pool , cooking there and wine tasting. We rented a car to tour the villages. Great wine country like Napa, California, but with amazing churches! I loved Cathedral di Sienna! Google it. Slow paced country villages with gorgeous rolling hills.
Southern Italy...Along the Amalfi Coast we like Sorrento and a ferry to Capri island. Love Capri island and you can stay there. Naples airport. Two train rides. A little more difficult to get there, but the coast is AMAZING!