Cinque Terre & Tuscany Itinerary

If you were to fly into Genoa, the train ride to La Spezia, from which you can travel to the villages of Cinque Terre by train or ferry, is only 1 1/2 hours.

We flew through Florence and the train to La Spezia was an easy connection.

For Cinque Terre, it's possibly enough - depending on what you're interested in doing. To see the villages and get a flavor of the area, yes. If you'd like to do a lot of hiking, time at the beach, etc....you would just have to prioritize. Research the villages and pick your favorite 1-2 to focus.

Tuscany - a lifetime is not enough. If you must do it in 4 days, don't plan to do too much, so you can relax and just enjoy the atmosphere at a slow pace. We stayed in the Pienza area and loved it.

From my origin I usually have one or two big-city airports I can fly into at a reasonable cost; the others are often much more expensive (like $500 extra). Your situation may be very different, in which case you might not be limited Rome/Milan. I wouldn't make a decision about the first night until I had deteremined my destination airport. You might be able to move on to either Cinque Terre or your Tuscan base the same day you fly into Italy, depending on whre that flight takes you.

I must be sounding like a broken record (I trust you know what that means) to regulars on this forum, but I have to say that the CT are not worth almost as much time as Tuscany. The former are small, insignificant villages. The latter is a very large, highly varied region, of enormous historic and artistic importance. Think Etruscans to Renaissance and beyond.
There are many attractive Tuscan towns offering “something for everyone,” wine tasting, food tours, natural hot springs, beaches, not to mention art in museums, churches, and outdoor sculpture parks. I have lost count of how many times we’ve been there and still not seen it all.
While July is high season in both areas, the CT will be crowded beyond belief.

I visited both areas you're thinking about this past summer and came from Florence. I would try to fly in to either Florence or Pisa to get as close to CT so you aren't spending so much time trying to get there on 7/24. I did three nights in Vernazza and found it to be just enough. It does rain pretty often, so be ready to be flexible about your plans. I would definitely suggest driving through/to Tuscany, since the drive is the best part of that area. I took the train from CT down to the Pisa Airport and picked up my rental car from there (Sixt). I drove down to Volterra and spent two nights there and then two nights in Siena and finally two in Montepulciano. Of course you only have four nights total. The best views were the drive between Siena and Pienza/Montepulciano. It depends in part on whether you want to stay in a little hill town like Volterra, San Gimignano, Montepulciano or Pienza, versus a bigger city like Siena. I liked all three places I stayed for different reasons, it's just based on what your priorities are.