What airport to fly into

You don't say what airport you are flying from, but assuming O'Hare (since you're in Illinois), the only options for direct flights to Italy are Rome and Milan. (Also Naples, but that's farther from where you're going.) If you are okay with a layover, you could fly into Florence, which has direct flights from most of the major cities in Europe.

Assuming you are coming from Chicago, United has direct flights to Milano Malpensa.

What is your reasoning for not taking a direct flight to Rome and then taking the train to Tuscany?

Fly into Venice or Florence but it’s going to include a connection not be a direct flight.

Tuscany where? That’s a large region. Some areas of Tuscany are midway between Rome and Florence.

Since you're going to be mostly in northern Italy, my suggestion would also be Milan.

You might consider starting in the Cinque Terre, as it's relatively easy to get there from Milano Centrale. If you're staying in Monterosso, I believe there's at least one direct train in the early afternoon (I haven't checked the current schedules). It's also easy to get from the C.T. to Florence (the capital of Tuscany), often with just one change in Pisa.

You’ll probably find more choices and the best prices flying into Milan.

Try to see if Delta still flies from JFK to Venice. My wife and I went DTW -> CDG -> VCE. I was shocked to see a Delta jet parked at Venice. Looked it up and found that Delta started to fly direct from JFK to Venice again.

We did a great tour of Tuscany and Umbria last year.
We flew into Rome and took the train to Siena where the tour began.
If we wanted to fly into Florence, it would have involved visiting another airport for a transfer rather than a direct flight.
After doing Tuscany, you can take the high speed train to Venice and do an open jaw (land in Rome depart from Venice).