Italian Itinerary

Are you locked into flying in and out of Milan? If not, consider an open jaw option to avoid the zigzagging. Fly into Rome and start your itinerary there. Then Florence/Tuscany, then Cinque Terre, then Venice, then Lake Como, then fly out of Milan. There might be better alternatives; check Rome2Rio.com to get a good idea of travel times between different places.

I think it's generally better to plan your trip by thinking about nights rather than days. Then you will have a better idea of how travel time will eat up the time you otherwise would have included in a specific location.

Be aware that travel to smaller "countryside" places without a car is going to be more challenging and/or slower that travel between larger cities/hubs.

Otherwise, you do have a good mix of sightseeing in cities with great museums and such plus relaxation time. Enjoy! And congratulations on planning an independent trip for your first European adventure!

I think you are spot on when it comes to planning a relaxing journey over 23 days. I second Lane's thoughts on an 'open jaw' ticket, into Milan, out of Rome. With 22 nights I would go something like this ...
Milan (2)
Lakes (3)
Verona (1) worth a stop along the way
Venice (3)
Florence (3)
Cinque Terre (2)
Tuscany (4) without a car perhaps choose from Lucca, Siena, Orvieto - 2 nights each
Rome (4)

On day 13 you will eat up significant time getting from "somewhere in Tuscany" to Rome, so your 3 nights in Rome will leave you with very little time in Rome to actually do/see anything. 3 nights in a location usually = 2 days to do things, but in this case because of the travel time to Rome, you will have even less time than that.
Same thing for Venice because of the travel time between Rome and Venice (packing, checking out of hotel, getting to train station, waiting for train, then same thing on the destination side).

As others have mentioned, if you've not booked your flights, you may consider getting open-jaw ( multi-city) flights to avoid backtracking.

If you've already booked your flights to/from Milan, then you may want to go straight to Lake Como (via train) or Venice on the day of arrival then leave Milan till the end of your trip.

Here is a suggested itinerary:

• Arrive Milan then travel to Venice (3 nights)
• Train to Florence (4-5 nights) with day trip to Siena
• Train to CT via Pisa if you want to see the leaning tower (3 nights)
• Train to Rome (4-5 nights) with optional day trip to Orvieto
• Train to Varenna via Milan( 3 nights)- if you choose to stay in Bellagio, you can travel there by ferry from Varenna.
• Train to Milan (1-2 nights) then fly home.

I would subtract a night from Florence, and add a night to Rome.

I agree about counting nights rather than days; a night is a hotel stay, a day can be a couple of hours if you have lots of travel time (or if something goes awry).