I hired one in Puglia a few years ago, it was fine to be fair although the biggest city we went to was Lecce which wasn't that big, i wouldn't fancy doing it in the big cities.
As Sheaf says you need to be assertive and just pull out into any gap otherwsie you'll sit there for ages, also parking is weird as they seem to dump their cars in any gap there doesn't seem to be any set parking spaces, although that might be a thing in Pulgia as it's quite rural.
I dont remember a fiscal code but be careful and only use a reputable company as there are quite a few scam merchants in Italy would will screw you over heard some horror stories of people being charged thousands there for scratches and marks that were already on there but they hadnt checked the documents properly.
Where you heading? IMO the best country to visit in the world.