We visited Italy a bunch of times, including trips where we flew into Milan, before we actually visited Milan. Once we did visit, I found that I liked the city very much. Even so, for your first trip, unless you are really into Leonardo and his Last Supper, or into opera, I'd probably go straight from the airport to somewhere else (or fly into another city altogether, such as Venice).
I'd probably also skip Lake Como, unless you really like gorgeous mountain lakes and scenary (I didn't really like Lake Como, I thought it was boring, but I may be the only person who thinks that).
I would definitely add time to Venice - you currently only have 2 nights, one full day, there. There's a lot to see there, and it's easy to avoid the tourist crowds.
If you want to stay in rural Tuscany, further south than Chianti will be more centrally located (unless you really love Chianti wine). Try to spend more than one night in the Cinque Terre - a very long drive, and that area deserves more time.
I think renting a car as you leave Venice makes a lot of sense - we've done variations on that several times. Driving to and in Ravenna is easy. The mosaics of Ravenna are amazing; one of my top-ten made-made sights that I've ever seen. If you like Renaissance art, consider more time in Florence than just a day trip.
If you spend 3 nights in Cortona, and then go to Rome, you could also drop your rental car in Orvieto, and take the train to Rome from there. Also, where do you intend to day trip to? If you plan to day trip to Umbrian towns, you might want to stay further south (Bavagna, Spello, etc.).
The CT is out of the way of the rest of your trip. Another itinerary possibility: Drive Venice - Ravenna - Cortona - Tuscany, and fit in the CT then, though you're still out of the way for ending in Rome.