Ideally speaking
Buongiorno,
Sounds like a wonderful trip - and they are all very beautiful towns to concentrate on.
Bologna - 1 - 2 days
Florence - depending on what interests you the most (markets, shopping, museums, history, etc) you can easily spend 2 - 4 days in Florence....and within that time period you could include a train trip out to Pisa to break it up a bit. )
Pisa - if you are just talking about the tower and the Cathedral, then a half day is plenty. However if you want to explore the city as well
count on a whole day. You could also look at doing Pisa / Lucca in a day.
Siena (and area) - I would suggest moving out to the countryside for this and basing yourself in either a
B&B or maybe an agritourism near a small city center where you can have access to the buses. Siena is a lovely day trip and the countryside can be broken up into Chianti, Val d'Orcia and the coast.
Rome is a huge city --- and like Florence or the Tuscan countryside you could potentially spend weeks there exploring all it has to offer!!! However, you can also spend 2 - 4 days there (again depending on what attracts you the most shopping - museums - culture) and see quite a bit of what the city has to offer.
Buon Viaggio,
Donna Denise