<<I felt that 2 days in Florence might be too much>>

This is definitely not true!

<<I think that 1.5 days should be fine in Venice>>

Also definitely not true!

What has given you these ideas? I agree with numerous others who have tried to make you understand that you don't have time for ANY daytrips out of these cities. You will barely have time to scratch the surface of each one. I wouldn't try to do three places in seven nights, but if you insist, at least do yourself a favor and stay in the cities.

I have a bit of different view, but I prefer contry to city. The great thing about the time of year you are traveling is that you will not run into the massive number of tours and hords of people in the citys. I think that 1 full day in Venice is plenty. Florence would depend on how much time you want to spend in museums. If you are not a museum person, then one day in Florence is also enough. An ideal way to see the country would be to rent a car out of Florence (the airport is the best location for a quick and easy exit). You could then drive south on S2 to Siena, hill towns, pienza etc..... stay on that road until in joins A1 around Orvieto. You can take the car back to the Rome airport and grab a train into town. Your time in Rome again depends on what your interests are.... anybe Pompeii sounds more interesting to you. I would not go to sorrento or capri because of the time of year and they are way out of the way for you.

" If you are not a museum person, then one day in Florence is also enough."

I respectfully disagree. While Florence has some wonderful museums, it has much more to offer and that is not why we return again and again.

Thanks ppl for the inputs!!!
I am planning to not plan any day trips in advance. Once I start exploring the cities I would decide whether to go for a day trip from Florence/Rome.