The weather in Italy in November is typically very rainy at the beginning of the month, then getting cold later in the month.
I don't know where you write from, but you have a long vacation (4 weeks), and you use the term 'hiring a car' instead of 'renting a car', which makes me suspect that you write from Australia. I don't hear North Americans taking such long vacations unless they are retired and Americans generally say 'renting a car' rather than 'hire'.
Temperatures are typically in the 10's centigrade (50s and 60s F) during the day, but drop at least 5 degrees Celsius (10 F) in evenings and early mornings. It may also be damp and somewhat foggy, especially in the mornings and night in the valleys and along the seashores.
So the weather in Southern/Central Italy is like Melbourne or Tasmania in June/July. In Northern Italy even slightly colder. Italy has lots of mountains too, so temperatures drop considerably at higher elevations.
The days are short too, because Europe sets their clocks back to Standard Time the last Sunday of October, therefore it's dark by 5pm or shortly thereafter.
In that type of weather, it is indeed better to stick to cities and towns. There are plenty of great cities to choose from from Venice, down to Florence, to Rome, and all the way to Sicily (where temperatures will be better, but still not beach weather).
Hiring a car is not really necessary to visit cities and towns, as these are all well connected by trains and have very efficient public transportation options (metro, bus, taxi, trolleys). A car is also a nuisance to have in cities, because of traffic and parking restrictions in the city centers. If you plan to hire a car, to visit the country side, do so only for that purpose for the few days you want to do it. While having a car, it is best to stay in smaller towns or outside the big city centers where cars are not allowed. But overall I would limit car hires to only visiting smaller towns of Tuscany and Umbria. Those are enjoyable in winter too, and having a car for Tuscany and Umbria, while you visit those small towns, makes it more efficient. So out of your 4 weeks, take about a week, between Florence and Rome, to hire a car for that period and roam around Tuscany and Umbria. It's more efficient to choose one or two bases to avoid changing hotels too often. For Tuscany I recommend as a base some town in the Colle Val D'Elsa to Siena corridor (which is near the freeway. Siena works great too, but make sure your hotel is outside the ZTL (Restricted Traffic Zone in the city center).
For Umbria I recommend to stay near Assisi. Without a car, Perugia (Umbria's capital and transportation hub) may be better, but if you have a car, Perugia gets busy since it's not a small city.
Spending 8-10 days in Sicily, would be good too. It's far, so you need to fly there from Rome. Main airports in Sicily are Catania and Palermo. Try not to have a car while in Palermo (or Catania). Traffic in Palermo is the worst in Italy, and probably in Europe (after Istanbul).