In Italy, and Europe generally, a car can be useful for exploring small towns and the countryside, but in large towns and cities a car is nothing but a very expensive nuisance. Also, visitors are not allowed to drive into the centre of almost every settlement in Italy: see driventoit.blogspot.com.au
How much time do you have? And do you want to stop in cities or stick to the countryside? This is very important because in nearly every Italian city, the inner cities have zones called ZTLs where non-residents are not allowed to drive. There are plenty of discussions on the Italy forum started by people complaining about the fines they received for driving into these ZTLs. If you intend to avoid cities, then driving would be fine. But if you want to visit cities, then taking trains will be better.Edited: 04 August 2018, 10:31
Why on earth do you want to drive? It is long, expensive and boring. www.viamichelin.com will give you routes and costs. If you rent a car in France & drop it in Italy there would be a drop fee of several hundred €. What is your aversion to flying, which is both the cheapest & fastest way to do this trip? There are buses, but that would be long & miserable. I don't see the point in driving in Italy where the high speed train is much faster than driving & cheaper. Other posters have already warned you about the problems of taking a car into cities in Italy.
In fairness to the OP, my wife and I have had four very enjoyable driving holidays in Italy, but we prefer the smaller, less visited places. When staying in a town, we have always been able to have arrangements made so that we can drive into the centre. Driving the country roads in Italy (not the autostrade) is very enjoyable.
look at google maps and plot a course and then look at distances and drive times. Then pad the numbers with more time.
If you want to drive, go for it but realize all of the info thats been given.
I havent driven on any of my trips ,yet because i dont care to. But no one will stop you from doing so. You may think that everywhere else in the world is like your town where everyone drives. But its not. So consider WHY you want to drive and go from there.
heres a website for you to ponder.
alot of great train info, if you want to take it.
You can aways rent a car after you get to a town or whatever too.
here are my observations on my travels in Europe. You may find that the towns/cities are not layed out like they are in the USA where they are in a grid type of system. You may find they dont have any grid system at all and roads will change names at the end/start of each intersection. You may find that parkings is a real B. You may find that fuel is really expensive. You may find that if you decide to rent a car in 1 country and drop it off in another country , it will be (more) expensive.
We have often rented cars in Italy when staying in small towns or countryside; organize the trip so that you do not have a car when visiting places like Rome or Florence or Milan but that you have one for the time you are in Tuscany, for example, if you have time to explore the rural areas. If you are just going to Rome -- don't bother with a car. You can't take it into Rome and you can't use it there. If you get lodgings in a Tuscan town as a base you may find that you can have parking arranged (we have done this and could drive into the ZTL to park) or you can park in the tourist lots that always ring these small towns and walk into the center to a hotel or whatever.
But don't bother if it is just for transit -- if you don't have at least 3 or 4 days to meander.