Before you get killed in this sub for posting some very general plans, let me jump in -

For 7-8 days, you have too many places on your list. I'd say pick two of Rome, Venice and Florence, or extend the trip to 12-14 days if you want to do all 3. Pisa is cool, but in the grand scheme, isn't worth its own stop on your first trip to Italy. A lot of folks do a drive by of the tower, and there are some cool buildings and churches, but it's not really a destination until you're really exploring Italy beyond the main cities.

For 7 days, I'd do 4 in Rome, 3 somewhere else. If it's 8, then do 5 in Rome. If you want to do Rome, Florence, Venice, I'd split that up as 5, 4, 3 (12 days total) if it were me.

Search this sub a bit - Rome, Florence and Venice are discussed extensively. Even if you limit it to the last 3-6 months of threads, you'll see a lot of good info on where to stay and what to do.

I know Florence better than other places in Italy. I can help you with that once you decide how long your trip to Italy is going to be and what cities you'll really visit.