If you're a reasonably good driver, there's no reason to think you cannot navigate your way through Northern Italy. I assume that you're flying into one of the Milan airports.
I would suggest you wait until leaving Milan to pickup the car. It's less than an hour to the incredibly beautiful Lake Como area. You'll do best to leave the car somewhere and take a local train into the C/T.
As in many mountainous areas, trains don't go to all the great tourist sights and cities. Northern Italy is best seen rambling through the countryside with a car. You can just see so much more, and be much more efficient in your travels. Roads are well paved and well marked.
If you fly open jaw out of another city, you may can take in other cities (Florence or Venice.) Many car rentals in Italy can be dropped off in larger cities without any drop fee.