Thoughts on itinerary

You need to carefully study the logistics of the morning you fly out of Venice. What time will you need to be at the airport? What time must you leave your hotel? Hotel website should help. You may want to stay near the airport that night.

Also research other transportation options in Bologna. Search this website for "car rental in Italy" and you'll see why I say this. We rented & drove with good results, but only after a lot of research and information. Check into bus schedules or taxi availability since Bologna is the only place you need a car. Understand that every transition (catch a train, rent a car, change locations) takes longer than you think and may not go 100% smoothly.

You've an ambitious plan but I understand it bc of the 15 year old. I remember those years well. The travelers of this forum will have valuable information. Listen to them - and your gut. You'll be glad. Enjoy!

Can you reverse your trip to start in Venezia? Departing from there can be very early and expensive (water taxi rather than vaporetto).

Unfortunately our airfare is already purchased. It was less expensive to depart from Venice. We still save money even with the private water taxi for the early departure.

Are you 5 nights in Rome so you really have 4 full days? That is important. if it is 4 nights and really 3 full days (arrival day from the U.S. is kind of a loss). My sense, if it is 4 nights is you would be short-changing Rome since you plan a trip to Pompeii as well. Instead of the Cinque Terre, maybe a little extra time in Florence so you can take some time to enjoy the countryside of Tuscany. It's going to be HOT everywhere you are visiting and you may not to be able to do as much as fast as you would like.

Cinque Terre is worth 2 days. and just do a day trip to Pisa. so you don't have have your bag in Pisa although I guess you could lock it up if there is space at Pisa Train station. Unfortunately you can't do everything Italy is an embarrassment of riches so count on returning there again.

I was also questioning the car rental day, although I am finding price quotes through Auto Europe that are partly cheaper than I expected - $50-90, depending on date, lower now and higher in August, with partial CDW.

If you could live with just one brand of car museum, then they're easy enough to reach by bus. I've only visited Ferrari (loved it), so can't compare them.

Lamborghini from Bologna train station: https://www.lamborghini.com/en-en/experience/museum

Ferrari museums (2) from Modena train station: http://www.vivaraviaggi.it/happy_circle.php?happy_circle=6

Do you arrive in Rome on Day#0 ?
I would try to avoid the car rental in Bologna.
Overall I think it's s great trip and you will have a wonderful experience.
Be prepared for a very hot time in Pompeii.

Thank you for all the great feedback! We arrive in Rome at 0915 on Day 1. We figure we'll be to the Airbnb by midday. We'll keep the touring light that day - Spanish Steps, Trevi Fountain, etc. Day 2 - Vatican highlights. Day 3 - Pompeii. Day 4 - Colosseum, Forum, etc. I'm on the fence about the Pompeii tour. The guys aren't overly thrilled about it, and it's a really long day of touring. Good point about the heat, too.

If we don't rent a car in Bologna, is it possible to still see both museums in a day (again, not factory tours) by public transports and/or taxi? Why should we avoid renting a car? We haven't rented internationally before - always used public transportation or car service. From the research we've done, it looks like we need an IDP and need to be aware of the ZTL's.

I'm on the fence about the Pompeii tour. The guys aren't overly
thrilled about it, and it's a really long day of touring.

Take a look at Ostia Antica as an excellent substitution? It's much closer to Rome so wouldn't be the grueling day that Pompeii would be, and gets glowing reviews from tourists who've done it: Here's what Rick has to say:

https://www.ricksteves.com/watch-read-listen/read/articles/ostia-antica-near-rome

But there's plenty to see and do in Rome to fill your 3.5 days if your gang isn't wild about this idea either.

Editing to add: do be aware that you need to pre-reserve your timed-entry tickets to climb the tower at Pisa to be sure of getting a spot during high season. IMHO? This is one of the things I'd probably skip.

http://www.opapisa.it/en/

regarding the Pompeii trip - I've been. We left Rome and stopped in Pompeii en route to Sorrento. It is an amazing and HOT place, but it was a lot of effort. My daughter and I are returning to Rome soon (hooray!) and we are going to Ostia Antica which many, including Rick, enthuse about. It is very easy to reach via train or bus. Read here for info on visiting OA from Rome. It's also covered by the RomaPass if you choose to go that route. RomaPass official site

If you will be in Italy on the first Sunday of the month, many of the STATE sites (not private or church) will be free.

I think we'll drop the Pompeii day trip since the level of the interest from the rest of the crew doesn't justify the effort for the logistics of it. Thank you for the options for alternatives. We'll check those out.

Rick has an audioguide for Ostia Antica.

There is a shuttle from Modena station to the Ferrari Museum.
https://musei.ferrari.com/en/modena

We had to rent a car in Bologna for the Lamborghi factory tour due to a strike in Emilia Romagna last year. The museum is across the street from the factory. You can take a bus to the museum/factory. We had no problem renting the car at a location near the Bologna train station. Since we had the car we drove to Modena to the Ferrari museum. There are plenty of buses in this area (I am here for 5 months now) but buses take a long time. The Lamborghini factory was wonderful and well worth the price. It was the highlight of the trip for my husband. He also liked the Lamborghini museum. I'm not a car person and the factory appealed to me more. He also really liked the Ferrari museum (I walked around town instead of touring museum). There is also a Ferrari Museum in Maranello near the factory.