A lot of people go to Naples by car, some because they have kids and a lot of luggage, others because they prefer the autonomy that having a car allows.
You can reach Naples by the A1/E45 highway, which connects Milan and Naples. The A1/E45 is also close to all other major highways and the Naples bypass. Thanks to this highway, reaching Naples is not hard at all, but beware that the traffic can be really heavy once you reach the city. The way in which native Neapolitans drive may be challenging at first, but you will get acclimated to it.
Be aware that in the city center there is a large Limited Traffic Area (ZTL in Italian) that does not allow cars during certain hours of the day. If you enter this area, you'll receive a fine that you'll have to pay even if you do not live in Italy.
Parking: On average, daily parking costs is 20 Euros per day.