A week trip to Rome and Tuscany - should I include Florence?

Start from the farthest point first and leave Rome for last if you fly out of Rome FCO. If you fly into FLR and out of FCO, even better.
Rome needs 3 nights at a minimum (4 better)
Florence needs 2 nights at a minimum (3 better)
Tuscany is a region larger than Massachusetts and Rhode Island combined. Florence is its capital city. There is no limit to the amount of time you can spend visiting those towns. Three nights (2 full days) would be good. But do you plan to rent a car for visiting Tuscany?

I'm coming from Israel, and as far as I know there are no direct flights to Florence from here. And I want to start with Rome anyway, so I'm likely to arrive in Rome and leave back home from Milan.

By at least 2 nights in Florence, do you mean between 1-2 days?

I don't have a driver license, so whether I rent a car depends a lot on who my partber will be. I might use the train.

4 nights in Rome gives you 3 full days, 3 nights in Tuscany gives you 2 full days as your first and last days are usually devoted to arrival & departure, so are you taking 7 days INCLUDING arrival/departure? If so, 3 full days in Rome and 2 full days in Tuscany really leave no time for Florence. Rome to Florence by hi speed train is easy; Tuscany without a car is tough; better perhaps, day trips to Tuscany from Florence.

What parts of Tuscany do you want to see? And what time of year are you going?

Please rethink your itinerary based on the good advice from Roberto, who grew up in Florence. Fly in and out of Rome, visit Tuscany first and end your trip in Rome. It takes at least an hour longer to go from Florence to the airport in Milan than to the airport in Rome; plus Milan isn't on your itinerary, so it's not the best choice for your return flight. You don't say whether you have 6 or 7 nights in Italy. With 6 nights, it's wise to choose only 2 locations. With 7 nights you could do 3 locations, but you'll loose a half day changing locations. Consider spending the first half of your trip in Florence and the second half in Rome. There are many easy day trips from Florence - Siena, Lucca, Pisa, San Gimignano, Bologna (not in Tuscany), often-overlooked Pistoia, etc. Also, without a car, staying in the Tuscan countryside could be a transportation challenge.

Douglas - including arrival and departure it would probably be 8 days. Hopefully arriving on Saturday and returning the next Saturday. Whether I have time for travel on the last day, depends on what time I leave (hopefully evening) and what I decide to do with that day. I only plan the trip for the autumn (summer's too crowded and hot) which is a long time to go, so the details are far from being set yet.

Susan - I haven't decided exactly which parts (there's still a long time to go, and you probably should leave things for flexibilty during the trip, especially in a rich area like Tuscany), but generally a want to combine a rural/green trip with a city trip. The trip is planned for September/October.

Frank - I guess you're right about flying in and out of Rome. For some reason I assumed Milan was closer. By the current plan I have 7 nights in Italy, but I'll probably have no tim for travel on the day of arrival. I'd rather start from Rome for a number of reasons, one of them is the fact that I don't want to have to take like a 3-hour ride from Rome to Tuscany as soon as I get in Italy (and also I may arrive in Rome around midnight). I'd rather take that ride before I leave. And let's hope I'll be able to have a car and make the trip in Tuscany easier, otherwise the idea of day trips from Florence seems the most likely. Right now however, I'm tending to give up on travelling in Florence itself, as by the current olan I only have 6 or 6.5 days netto.

You might then consider doing 1-2 days in Rome at both the beginning and end of your trip, with your Tuscany visit scheduled in the middle. Unless you have an afternoon flight from Rome or a car you plan to return at the airport, you should stay in Rome the night before your flight. Using public transportation, it's logistically difficult (in some cases impossible) to get from Tuscany to Rome airport in adequate time for a morning flight.

I actually plan on flying back from in the evening or afternoon, so unless I'll have to change that, I guess the transportation from Tuscany wouldn't be much of a problem. I don't know if I'll actually do travelling during that day, it depends a lot on the time of flight.

By all means go to Florence. An overnight stay will be fine. Enjoy the Uffizi; the Accademia; the Dome; the Baptistry Doors and the Vecchio Bridge (forgive any typos). It is one of the most exciting cities in Italy if not the world.