I lived in Torino for almost 7 years and I used to work for Lamborghini, so that area is quite familiar to me. Do not worry about narrow and bumpy roads, those are usually in the city centres where normal cars are not allowed to drive. Don't do it or you'll get plenty of tickets when you get back home. I can't really tell about accomodation but it is very easy to find where to stay. Regarding the itinerary, you should also check the Ferrari, Pagani and Ducati museum/factory. There are pretty nice roads to drive around Maranello, awesome driving combined with great views of the countryside and some Italian restaurants along the way. People over there is very nice and friendly but don't expect to find too many bars or pubs full of youngsters, because very few live there. Bologna is your best bet if you wanna do that, but not where the super car factories are. Not many people speak good English in Italy but they will do their best to help. There are some super car rental places in Maranello and Sant'Agata and the guys are usually quite friendly. If within the first minutes you show them that you can actually drive, they will let you floor it with no hesitation.
If the trip is not exclusively petrolhead related, Firenze, Torino, Sienna, Pisa, Como and Venezia are nice cities to visit. Roma would be great as well, if you wanna go that far. Milano is in my opinion the shittiest city in the entire country but if it's on your way it's worth a short visit.
Keep and eye while driving in Italy. It is absolutely fine when you get used to it, but for Italian drivers traffic rules are just suggestions and they barely respect them. This is more evident to southern you go. Watch out for speedcameras also. Especially the Autostrada towards Bologna it's full of "Tutor" which are the speed cameras that calculate the average speed between two points. If you go further south there are thousands of standard speed cameras although most of them are advertised.