In Milan we would recommend visiting the Cathedral + going to the rooftop (linked below), as well as visiting the Navilgi canal region for dinner and drinks! Milan is quite a large city, but easy to get around using the Metro. It would be a good choice to fly in to, if you want to extend your Italy holiday, and visit some of the Lakes also - Lake Como is a short train ride from Milan.
If you fly into Milan and hire a car to head to Villa Giulia, the route will likely take you past Lake Garda. Alternatively, you can hop on a train from Milan to Como for a couple of quid!
The Ducati museum is in Bologna - you can fly direct in to Bologna, or if you opt to fly into Milan this would make a good pit stop.
Misano GP is 'coincidently' the weekend before the wedding and just 35mins away from the wedding venue...
If you have time to extend your trip and have not been to Rome before then we would absolutely recommend it! One of our favourite activities in Rome was the Vatican Tour + Climb of St Pauls Basilica. We booked it through the GetYourGuide app (very handy for tours/trips in Italy!)