I'm at the beginning stage of planning a 9 day trip to taly next Sept/Oct for myself and my wife. We plan to fly into Rome. Take the train Florence, then on to Venice, then back to Rome for a stay and fly out.
I plan at this point to book the airfare first, then the hotels, then worry about the trains. Is that the best way to do it? I've planned a lot of trips and travelled a lot but never to Italy. Can we depend on getting a train between these cities anytime (more or less) we need it? I will book the trains in advance, but not till much neared time to travel. Thanks for any help/advice. Also, anyone still use travel agents these days?

Have you considered flying into Venice, taking the train to Florence, taking the train to Rome & then flying out of Rome? You will save a lot of backtracking time this way.

Is it 9 nights in Italy itself? If so, I would do 3 nights in Venice, 2 in Florence & 4 in Rome. It depends, of course, on your interests. If the 9 days includes your travel days, you may want to limit this trip to 2 of your choices.

You can book trains before you get to Italy, but I have always just made the reservations while there, a day or so beforehand. Here is where a travel agent can come in handy! You can walk into an agency in Italy and they can make trains reservations etc. for you on the spot. I have either not been charged (Rome, Cinque Terre) and charged a small fee (Venice) for these services.

There are plenty of trains between these major cities.

Consider an open jaw: into Venice, out of Rome. It usually doesn't cost that much more and would be well worth it not to have to track back to Rome.

Trains run frequently on all those routes. You really don't need to purchase in advance. Just buy your tickets when you get to Italy.

If you do a little searching on these forums, you'll find you don't need a TA for Italy's "Big Three". There are many hotel recs on these boards for all three cities.

I did a trip in June/july starting in Venice, ending in Rome. I recommend the reverse. Rome is so hectic, it would be better to start with the high energy, and slow down with the quiet canals of Venice (instead of the loud traffic in Rome) Both are wonderful, but I found I was exhausted with Rome in a short time. It was a rough way to end the trip.

The reason most people recommend flying INTO Venice is that transatlantic flights out of Venice leave very early in the morning. Transportation to the airport is very limited that time of morning.