How early to plan 2 weeks in Italy?

I prefer fall to spring in Italy, mostly because I've experienced too many groups of traveling high school students in the spring. So it depends on what kind of lodging you want. I've encountered them in budget hotels in Florence, Venice, and Rome. The noise levels late at night can be remarkable, and when I've complained, I typically get transferred to a teacher, who often doesn't speak English. If you stay at more expensive hotels this won't be an issue.

If you go in the fall you should book lodging as soon as possible for Italy. I found booking.com to be a really good source when I'm having a hard time finding lodging.

Before moving here I planned our trips at least a year out. :-) I liked to have a solid outline before I booked my flights. I would research how many nights I wanted to spend in a place based on what I expected to do and how long it would take. Then once I had my flights (331 days out with FF miles) I could start filling in the stays and secure my lodging. When I got to 3 or 4 months out, I would make high speed train reservations, buy tickets
for sites requiring advance reservations, tours, etc.

It is not impossible to do what you want to do in September, but it might be stressful and you might have to "settle" for lodging rather then get your first choice. Still, you can have a great time! I planned a last minute (30 days out) trip to Switzerland for New Year's. We were unable to get first choice on a hotel, but we "settled" and found a safe and decent place and had a wonderful time.

I've never been to Greece, but I do know that tagging Santorini onto your Italy trip will add a lot of time, money, and hassle. Unless you have a special reason for including it, it's much easier to do Greece and Italy as separate trips. If you feel you need more relaxing, you can easily add some time in relaxing destinations in Italy. For instance, you could go to the Amalfi Coast for a few days.

I was in Italy last month (mid-May) - Bologna, Florence, Assisi, Orvieto. There were school groups at some of the sights I visited, but I didn't notice them in the evenings. I guess if you're staying in the kind of accommodations that would be suitable for groups, it might be a problem, but that's probably not going to happen! I think mid-May is likely to be somewhat cooler than September. Umbria was so beautiful in the spring!

I would continue to plan now for September, and don't get you heart set on any particular accommodation choice. Cast a wide net to see what's available and choose between those. You won't spend much time in the hotels and they should not make or break a trip. Although September is still pretty busy, it's common to just show up and find a room in Greece.

The difference is more likely to be in price and/or location. When I planned my recent trip, prices increased - even at the same hotel - as my travel dates got closer. I found that out when I considered changing my itinerary - so I stuck to the original plan, luckily it was a very good one. The more lead time you have, the more options you have. You will either get good rooms for less money, or better rooms for the same money.

You shouldn't have any issue finding places in Rome, Florence and Venice now. Perhaps the CT though. I woudl contact some places you want to stay at there and if they have room take it and plan for september. If not and you have to settle for someplace in the CT you might not want to stay push it back.