I strongly concur with the advice to limit the number of cities. In the time allotted, I'd skip Venice on this trip (a city that doesn't have a number of "must-hit-once" attractions, but that must be savored and absorbed in order to really get the most out of it) and I'd skip Pisa altogether (a huge bore, frankly) and give Rome and Florence 2-3 days each, with one day in Milan to hit its highlights (especially the Cenacolo / Last Supper).

This will give you a flavorful introduction to Italy and it will whet your appetite for your next visit . Most importantly, this will give you and your wife unhurried time to enjoy each other's company in this fabulous country.

In all instances, be sure to make advance reervations (easily done either on the internet or over the phone) for the prime attractions, such as the Uffizi and the Academia in Florence an the Cenacolo in Milan. This will let you and your wife skip the lines and enter the attractions at your appointed time.