I live in RST, too. Small world.
I think Venice in early April sounds great. The crowds will be smaller and the patience of the locals with be longer. Weather will be cool; especially at night, but I think it's a great time weather-wise. Since it's your arrival port, maybe spend 3 nights there to shake off the jet lag. That gives you an extra day to dodge rainstorms as they pass through.
There will be multiple trains to Florence during the day so don't feel like you have to pick one that leaves super early. The two lines are Trenitalia and Italo. Check them both for best fit & price.
Florence: Warmer than Venice but still cool at night. Buy your tickets to any museums as early as you can. But if you do miss out, you can pay more and do a tour. I was pleasantly surprised how much I liked the tour of the Accademia through one of the big tour companies. Since you're from Rochester, you have to eat pizza at the Florence Mister Pizza. It's actually really legit pizza and the location outside next to the Duomo is ridiculous. I do have a hotel recommendation for you. DM me if interested in an awesome little place very walkable to the train station with a great view of the city. I'd book that place ASAP if you can. I might opt for a train trip from Florence to Sorrento. It might be a tiny bit longer but way more comfortable and just less hassle.
I expect Sorrento will be beautiful weather-wise. It's been so long since we've been to that area that I won't make any specific reqs. You could check flights home from Naples
And yeah, I would avoid Rome. Even though Easter isn't until later, it will be crowded. Plus you may experience unexpected closures as the city gets ready for Holy Week. I experienced this prior to the last jubilee.