Milan during fashion week

I cannot believe I didn't realize this but when my husband and I booked our trip to Italy 9 months ago, we will be in Milan right in the middle of fashion week September 25-28 (in a few weeks!). We do have our hotel booked and our last supper tickets. How crazy will restaurants be? Do we need to book places now? Can our hotel concierge help? One thing we don't have is any tickets (timed entry or otherwise) for the Duomo. I haven't been to Milan in probably 15 years so back then you could basically just walk up and get a ticket for the Duomo including the terrace. Should I book some sort of timed entry visit for that?