I would also caution against driving too far after a long international flight, a practice which has been compared to impaired driving. I assume you're aware that you'll need the compulsory International Driver's Permit for driving in Italy. These are used in conjunction with your home D.L. and are valid for one year. You can easily obtain I.D.P.'s for a small fee at any AAA office (Passport photos required, but those can often be supplied by AAA).
If you haven't driven in Italy before, you'll also have to be vigilant to avoid the dreaded ZTL (limited traffic) areas, as hefty fines will result for each pass through one! Do NOT drive in Florence as it's just about saturated with automated ZTL cameras. I just received a note from someone who received two ZTL tickets, which where eventually referred to a North American based collection agency. By the time the matter was settled, the cost was about $700! You'll also have to contend with speed cameras, including the devious Traffic Tutor on the motorways, parking, tolls, etc.
One option you might consider would be to spend your first night in Stresa. It's relatively close to MXP and a beautiful city. That would be a great place to have a good rest and start to get over jet lag. There are lots of hotels, good restaurants and you'd be able to browse the stores. Ask your hotel for restaurant recommendations (or possibly your hotel may also have a restaurant on site).
The Cinque Terre is not a good choice at this time of year. Many of the tourist businesses will have closed for the season, and the weather may be an issue. Parking may be a problem in all of the towns except Monterosso. There won't be much to do in the towns at this time of year, so not much fun wandering around a town that's mostly closed in the pouring rain. It would be best to leave that for a future trip at a more favourable time of year.