We rented from Europcar on Sicily 2 years ago, then ferried it to the mainland and drove up to Sorrento. That part of Italy had no tolls, so I can't offer advice.
We checked with our Visa card company and decided to use their insurance coverage, and we waived any extra insurance from Europcar. We didn't have any accidents so we fortunately didn't have any claims to file. Check with your credit card bank to see what they cover, what deductibles and paperwork would be involved in the event of damage and see what will be the most convenient and cost-effective for you. Sometimes peace of mind is worth some added insurance expense.
Rick Steves even says he's driven without an IDP, and some dubious folks would even argue that "you're not guilty unless you get caught," but if you do get stopped by a cop and don't have one, the penalties are pretty harsh. It's better to be in compliance than to save $15 or $20 at the start of your trip. You can get the IDP at AAA even if you're not a AAA member, so it's cheap "insurance" to have the IDP. It's good for a whole year, and other countries, like Austria, also require it. You will need 2 passport-sized photos for it, or AAA can take the photos for you. Each driver needs their own IDP.
The autostrade thru Calabria had a lot of construction zones, so the highway was down to one lane in places and passing sometimes wasn't possible. People were courteous and also for the most part didn't speed. However, Audis, BMW's, Mercedes, and Volkswagens did zoom past other cars, even when everybody else was driving the speed limit. Maybe there's some unwritten rule in Italy that if you have a German car, you have to pass Fiats and Peugeots. We didn't want any speeding tickets, and this forum is full of reports from people who got home from a trip to Italy and got an expensive ticket in the mail months later, forwarded by the rental company.
Also, make sure you know whether you rental car is unleaded gas or diesel. So you can pick the correct gas pump for refueling, gasoline in Italy is "benzina," and diesel is "gasolio."