Critique my itinerary

Is there a reason you are visiting CT before Florence and backtracking like that? Is it due to days of the week lining up (so that sights in Florence are open)? Or there's possibly a certain overnight train you are looking to catch? Or are you looking to split up the cities with a more outdoor/town-like setting? I just ask, because if none of these apply, then I would recommend doing Florence before Rome because otherwise you are just backtracking and spending that much more time on the train. And if the reason for it being as such is that you're looking at an overnighter from Florence, I'm sure there's an overnighter you could catch from Genova, which is near CT and still on the way to Paris. That way you're always heading in the right direction and not back tracking.

Just an initial thought.. otherwise I like how you've split your time. Have fun!

I read on another website (I think about.com) that it was easiest to go Rome-CT-Florence, but I haven't really checked into it. We chose this way mostly because we wanted to split up the "city" time. It has been years since I visited Rome but I remember it being kind of overwhelming. Now that we're older and have traveled more that feeling might be diminished.

I haven't looked at the train schedules in earnest, but I also assumed it would be easier to get a train to Paris from Florence than from CT. Geographically, it does make sense not to backtrack though! I will have to check that out.

Yeah I'd check that out. The only reason I would think to train to CT before Florence would be if you are going to Venice afterwards. But otherwise, it would make sense not to backtrack. Training from Rome to Florence only takes an hour and a half on the Eurostar. Training from Rome to CT takes at least 4 hours. From Florence to CT is 2.5 hours, and Pisa is on the way, so you can stop and sightsee there for a break mid-way.

You can look at the TrenItalia website for Italy train schedules, and you can check the Bahn website for international train schedules. But I'm sure there's a train from Genova to Paris.

So, just so you don't backtrack, I'd go to CT after Florence, unless of course you want to split up Rome and Florence with a small town stop, or there's a better train schedule to Paris from Florence or something. But be sure to check out Rick's guidebook (or some other guidebook) and make sure you will be in Florence on days when the sites are open (because the museums are closed certain weekdays). So this could also come into play in deciding which stop you will make first. Either way, enjoy!

If OP needs to end in Florence, why go from Rome to Florence to CT and BACK to Florence?

Instead of CT, maybe stay in Rome and take a day trip to Ostia Antica or Hadrian's Villa. Then add a day in Florence for a day trip to Siena.