1. Lake Como doesn't close. You can just drive or walk up to it. However many of the hotels on Lake Como are only open during high season. IMO it requires more than a half day. It's nice to drive the whole way around the lake and stop in a couple small towns. It's also nice to get a view of the lake in different light.

2. Pompeii is near Naples (and the Amalfi Coast, and Capri/Ischia). It's far from everything else on your lists. In summer, the best way to see it is to go as early in the day as possible, before the sun becomes too hot.

3. Assuming that Italy will be less crowded than usual with tourists, cruise ships and their passengers, this might be a good time to see places that are normally extremely crowded or ruined by the presence of large cruise ships and their daytime hoards.

4. Rather than trying for a checklist of the top sights of Italy, focus on a region. For example, you could focus on Tuscany and go to Florence, Pisa, Lucca, Sienna, San G. or some of the smaller hill towns, etc. If you want to see Venice (tourist trap but I guess it's something that everyone should see once), also go to Bologna (beautiful old university town, now known as a foodie place) and Modena (food, including truffles!); Verona would be along the way if you combine this with Lake Como, and there's a pretty wine producing region east of Verona. If you go a bit south from Bologna, there's San Marino and the smaller Italian city known for the historic church with the inlaid floor (sorry, but the name escapes me at the moment).

5. Remember that Italy is strike prone. Expect travel to be disrupted in some way by a day of a general strike, train strike, public transit strike, strike by different categories of airline and airport workers, etc.

6. Do you plan to rent a car or use trains? Trains make sense between larger cities and for day trips to nearby smaller cities, but you almost need a car for Lake Como, wine villages and IMO the Amalfi Coast. If you're not accustomed to driving in Italy, IME the northeastern region is the easiest but of course you can't take a car into Venice.