From Venice on way to Rome--stopover in Lake Como or Cinque Terre?

kb,

Lake Como would be somewhat of a detour, however a short visit to the Cinque Terre would work and it's easy to get to Rome from there. Which of the five towns are you thinking of staying in?

There are numerous trains from Venice to the Cinque Terre each day, usually either via Milan or via Florence. The trip usually involves at least two different trains so changes will be necessary.

When is this trip taking place? It could be difficult to get room bookings in the Cinque Terre on short notice.

As you haven't travelled in Italy before, you'll need to do some homework on using public transit there as there are some potentially expensive "caveats" to be aware of. If you need more information, post another note.

First of all one night only in Venice is too little, especially considering you will be jet lagged the first couple of days. You should spend at least two nights in Venice (3 even better). Two nights in Rome are also inadequate, because that gives you only 1 full day in Rome. Lastly, if you look at a map you will notice that Florence (Tuscany) is in between Venice and Rome, therefore it would make sense to go from Venice to Tuscany first, and THEN down to Rome. You don't have time for Lake Como, also because it's a major detour. At most you could take a day trip to the Cinque Terre while you are in Tuscany.
You have 9 nights on the ground in total. The sequence should be:
Venice 2 nights
Florence/Tuscany 4 nights
Rome 3 nights.
If you want to spend nights at the Cinque Terre, you should insert those between Tuscany and Rome. But I don't think you have enough in total to spend nights there. I would do a day trip from Tuscany.

Roberto is right, the day you arrive you will be jet lagged so you won't do much that day, except maybe go for a stroll and eat dinner.

So one night in Venice is not enough time to see all the major sights there.

If you only have 9 nights in Italy, and you're meeting friends in Rome, I'd fly into Rome and spend 4-5 nights there before heading to
Florence/Tuscany.
Keep in mind that spending 2 nights in Rome means that you only have one full day to explore Rome.

Edit: If you are set on visiting Lake Como or The CT, I'd skip Venice and fly into Milan to visit Lake Como or fly into Pisa to visit CT.

I've learned two things on here about Italy. 1. Listen to Roberto, 2. Listen to Roberto.