I don't know what, "I would plenty in Venice" means. It's not a city you can see in just a few weeks. Maybe you can get off of a cruise ship and see Piazza San Marco in two days, but you certainly can't see the world's most beautiful city in 2 days.

Four days Florence and Tuscany is also too much. That's just running around from place to place. I'd suggest staying in Florence and choosing one Tuscan town for a day trip. Tuscany is a region, similar to what is referred to in the USA as a state. Saying you'll visit Tuscany is like saying you'll visit California. No one knows what that means.

There are a lot of crappy fake villages around Florence that are open for 8 months out of the year and prosper by serving what peoples' images are of Tuscan life, but it's so theme park touristy. Definitely stay in Florence and choose a nice small town to visit outside, but beware of the italian theme park industry there. I find Tuscany to be the least authentic part of Italy.

I'd trim from Tuscany and Amalfi and add more to Rome. Rome, like Venice, is one of the world's great treasures and fascinations. Even when you are looking at it you can't believe what your eyes are seeing. Or, take a day off of Tuscany and visit Naples for one day. That's the real Italy. Naples is not a theme park. That's where you get to see real Italy.