Hi there, some excellent suggestions above. I was wondering about your dates and direction of travel - In general, I would suggest starting the furthest south and head north so early in the year. However, Easter is early this year! So anywhere, but especially Venice, Florence, Rome & small towns in the AC, will be JAMMED from Good Friday, March 29, through the following weekend April 7. (It seems Wednesday, March 27 is the beginning of Italian Easter school holidays, I just saw on a post about Easter in Venice.) I capitalized the word 'jammed' because we just spent 8 days in Rome over NY, 2023-24 and seriously, it was the most crowded I've ever seen it, and I've been going at the holidays many times over the NY.
So personally, I would either be ending my trip by Good Friday, or arriving the weekend of April 6-7, but guess what, more people will be traveling in April than in March...
Arrive Venice (3 nights), Bologna (2 nights), Florence (3 nights)
I like to think about actual transit time, (I'm a detailed planner) so would sit down quietly with at least google maps & hotel /apartment ideas and think about how long it takes to pack, get transport to train, add 15 min for screw ups, get train to next destination, blah blah, you get the picture!) So consider how long it will take from your hotel in Venice to place in Bologna? So you'd arrive there in the afternoon, making it really 2 nights but only 1.5 days before taking the train to Florence... and so on.
I've been to both areas several times & personally, I would go to Lake Como after Easter holidays are over & stay in Varenna, an area of superlative beauty & you can move around easier than on the AC. My niece was there last year in early April and had great weather, but of course that can vary! Like someone else said, you probably won't be jumping in the lake.
You would need to work on the logistics for AC more, if you do, consider staying in Salerno rather than Sorrento (which technically isn't the AC). And 3 days, hmmmmm. That's at least 6 hours I think to get from Florence to Sorrento, or Salerno, go out for the evening & relax, day 2 ferry along AC, day 3 via Pompeii where I understand there is small luggage storage available, train to Naples & train back to Rome, then logistics of getting to your hotel. (We did this last leg from the town of Amalfi with a private driver via Pompeii who kept our luggage while we walked miles, then delivered us to train in Naples to get back to Rome.)
Good luck & please come back with more details, always interesting to see the evolution!