3 weeks in September

Two nights in a location means you'll have one full day there. You're doing a lot of location changes which is going to eat up a significant portion of your trip. You lose about half a day when you change locations so it's always best to keep it to a minimum.

You have 9 locations listed for 21 days. That's a ton of moving around.

I would spend the first night in Verona. Leave late the next afternoon for Milan. I would add at least a day to Florence and visit Capri as a day trip. I wouldn't add any other stops or day trips. As it is, you don't have enough time in any location to really see much of anything.

Donna

I would start by shaving 1 or 2 nights off Venice (maybe at the end?), eliminating Milan, and seeing Verona as a day trip from Venice. That would give you at least 3 nights for Como or the Dolomites. If you omit the Cinque Terre, you could do both of the latter, each of which is more beautiful and more interesting than the CT.

Consider adding at least a night or 2 to Florence. 2nights = 1 full day. It needs more to do it justice. You can do a day trip to Siena from Florence.
We found that spending 1 night on Capri would have been a good idea. By the time we got there, got up the mountain from the marina, and later left time to get back down for our return ferry, our day felt very rushed. I don't think 2 nights is needed.

I would fly open-jaw or multi-city into Venezia and out of Roma. Or fly into Milano, spend the night and take an afternoon train to Venezia.

Spend four nights in Venezia and see Verona (and possibly Padova) as a daytrip. One night on Capri and throw your two saved nights into Firenze and Lago di Como.

Agree with the others...way too much moving around! If you have to fly in and out of Venice, I would fly in, but go straight to another destination. Since you are flying out of Venice, save your time there for when you will be leaving, 3 nights.

Since you want to see Lake Como, maybe go directly there to Varenna 2 nights. Then onto Cinque Terre 2-3 nights, Florence 3-4 nights, with day trip to Siena. Or stay in Siena and day trip to Florence. They are so close (quick bus ride) it doesn't make sense to stay in both. Also Lucca is very nice as a day trip. Then Rome 4 nights, and Sorrento 4 nights, with day trip to Capri. Return to Venice, with day trip to Verona, and fly home.

Don't waste precious time checking in and out of hotels, and traveling on trains. Stay put for a few days!

If you can fly open jaw. If you already have a round trip ticket to Venice then land in Venice and proceed to your next stop that day. As others have said, you need to cut some overnight stops or else the trip is all logistics and very little being there. I would drop Milan entirely, and Capri -- do Capri as a day trip from Sorrento if you must. Florence is not worth a two night stop; that is a place to add a couple of nights as it is dense in artistic treasures that take time to see. If you dropped Milan and Capri and the first two nights of VEnice that would free up 5 nights -- Add two to Florence, one to Rome and one to Venice and perhaps one to Sorrento with a plan to visit Pompeii and the Amalfi coast and Capri from there. Packing up, racing to trains, traveling, disembarking and checking in and out of hotels gobbles time. A night in a place unless it is in transit gives no real time to see and do anything. so maybe one night, the first night in Verona, but then concentrate for longer stretches.

Thanks for all the response. I'm looking at a couple different options. My airfare is booked. I normally would fly open jaw but we got a great deal in and out of Venice. I Love Venice so I'm not too upset. We are getting into Venice around 5pm so I think we should stay one night then head out. I think I'll take out Milan and Verona but my travel buddy wants to do the Cinque Terre. If I can only do the Dolomites and Lake Como which one?? I can do 3 nights somewhere between Venice and Cinque Terre. Thanks again!

I think I'll take out Milan and Verona but my travel buddy wants to do the Cinque Terre. If I can only do the Dolomites and Lake Como which one?? I can do 3 nights somewhere between Venice and Cinque Terre.

I think you can do both Lago di Como and the Dolomites, but skip going all the way to Sorrento. You just do not have time for it all.

Arrive Venice - 1 night due to late arrival

Transfer to Varenna/Lago di Como - 2 nights

Transfer to Cinque Terre - 3 nights (really worth staying 3 nights because it is so far to travel and also if you have bad weather one day, well, it's better to have a little more time. Plenty to see. Post again if you need ideas.)

Florence - 3 nights (So much to see and such a lovely city!)

Rome - 4 nights

Dolomites - 3 nights (Minimum time. If you do not have three nights, don't even try)

Back to Venice - 4 nights, day trip to Verona

Think the trip works much better including the Dolomites and Lake Como by eliminating anything south of Rome
Makes logistics and travel distances much less!
Save south of Rome for another trip
Your current plan requires a travel day of getting from a hotel in Capri all the way to a hotel in Venice, that is not going to be easy and will take a full and tiring day to do. (I guess you could fly from Naples to Venice and make things easier by doing so)
Neither place is good with bags though, which is why I envision it being tiring.