While Italy is my favorite part of this trip, but it’s not worth the time to go to Italy from Northern Europe just to spend 3 days there — your flight probably leaves in the morning, so the 11th is totally shot. Option 1, stay in Northern Europe and add Bruges. I’d cut time from Paris and perhaps Amsterdam and add 1 day to Berlin. You could probably squeeze in another city, or some nice day trips from Paris. If you have to take the flight out of Milan, take an overnight train to Milan on the 9th, spend the 10th in Milan and then catch your flight home.

Option 2. (my recommendation) Cut 3 days from Paris and 1 from Amsterdam. Add the days to Italy: Florence and Rome. Milan is worth a day, but I’d rather spend an extra day in Florence or Rome or on a whirlwind “day in Venice.” Take an early train from Florence to Venice on the 10th. Spend a 7-8 hour day in Venice and catch the 18:45 EurostarItalia (there are a couple of later trains if you happen to miss that one) to Milan. You’ll arrive in Milan at 20:25 — just enough time to get to your hotel or hostel for a beer and a comfortable night’s sleep before your flight home. You could also do this whirlwind Day in Venice with option 1. Take the overnight train from Paris to Venice.