11 days in Italy - review my itinerary

There's not nearly enough time devoted to Venice - which is a city quite unlike any other. Yes, it does seem quite rushed with very little time at your destinations yet a lot of time devoted to sitting on a train. It's usual for 1st time travelers to want to see and go as much as possible. You'll see "more" if you go "less".

But I will say Bravo for being very smart in not having a rental car in the big cities...and especially not having it in Venice!

I think it works but any chance you can add just 1 more day for Venice? I assume you have a long and likely not even direct journey in the air to reach Venice, with the time change and all of the uncomfortable time in the plane you are going to wish to have time to take things slowly the first day and a half which you plan does not allow for.
1 more night in Venice would help greatly, but don't see where else you can lose a day so would need to add to the total trip time.

Where are you renting your car in Pisa? May be easier to take the train to La Spieza (closer) and rent from the city offices there,
Not sure either location has rental cars that close to the train station. Maybe you were wanting to see the Tower/Marconi Piazza before getting the car, which if you pack light I guess is an option with Pisa.
Many towns will work for Tuscany with a car: Siena, Montepulciano, Pienza, Montalcino, San Gimignano, Volterra, Cortona, Greve in Chianti, San Quirico, Lucca, Monteriggioni, Arezzo ; any of these really could work for you, it is advised to research each and every one of them perhaps you will fall in love with 1 over the others.

I agree with the above posts. I would try to add another day to Venice.

Sorry to say, but you need to drop something. This is just too much in too little time. If you drop the Cinque Terre and add a night each to Venice and Florence, it will be a much better pace. Rent your car when you are ready to leave Florence and also skip Pisa.

Where to spend your three nights in Tuscany is dependent upon what you want to see and do. but I'd suggest heading south to Montalcino, a sweet a quiet little town focused on Brunello wine. You can take a beautiful drive one day to Pienza and Montepulciano. Don't miss the abbey of Sant'Antimo.

The only reason we're going to Pisa is to pick up the car. Day 6 is a Sunday, and most car rental agencies are closed, except ones at airports. Therefore, we'd take the train to Pisa Centrale station and a bus/cab to the Pisa airport. I understand there's a shuttle running between the Pisa Centrale station and the airport while the People Mover (tram) being built.

I'd be hard pressed to drop the Cinque Terre... If we add a day to Florence, we could do a day trip to Cinque Terre. It's doable, but feels more rushed than the original itinerary.

I think it's good. I've done several quick whirlewind stops in cities for 1-2 days on a trip. They don't bother me. I can see more of the country that way and then when I go back next time go for longer in those cities. It's all what you want. if you don't mind about a day and a half in Venice then go for it. (Assuming you land some time around 8-9am you should be in Venice proper by noon.

For Tuscany I'd second what Laurel said about Montalicino. Loved my stay there and the brunello wineries around the hill town. The country side is beautiful and the other cities she mentions are all nice trips. You can even head up to Siena from Montalcino or after you leave Pisa.

One thing is maybe drop your Rental Car off in Orvieto instead of Rome. This way you don't have to drive around Rome. Orvieto is a simple 1hr train ride (no connections into Rome). Just check that your rental car place has a drop off there.

I agree with others, you may wish you had more time in Venice. I see you don't want to give up Cinque Terre (me either!) so consider this---

Arrive Venice - 2 or 3 nights, Venice is unique.
Next, Florence/Tuscany - 3 or 4 nights, area is similar. Either stay in Florence and do day trips, or stay elsewhere in Tuscany and day trip to Florence.
Cinque Terre - 2 nights, also is unique.
Rome - 3 nights

Remember, you need time to enjoy yourselves, not just rush through towns!