"without a car, you won't be able to get into the Dolomites proper"

Well, actually, you can. You can take a bus up to Castelrotto, and from there you can take ski lifts to go hiking. Been there, done that.

I agree with the others about slowing down, but I would keep the lakes and the Dolomites and drop the Cinque Terre and Assisi and Orvieto. Maybe Siena, too. But that's personal choice.

Thank you for your advice everyone.. I really appreciate it!

>>Well, actually, you can. You can take a bus up to Castelrotto, and from there you can take ski lifts to go hiking.<<

Even if the lifts around Castelrotto are open in May, that's a lot of effort to go through just to hike around in the slush for a few hours. May isn't really hiking season in the Dolomites.

I love the Dolomites, and I've actually spent a lot of time there in May (biking, not hiking), but I would not recommend that area as a one-to-two-day stop in May for someone without a car (or a bike).

I agree with the advice about the Dolomiti. May is really not the time to make all that effort to get there.

A lot a backpackers who have taken across Italy trips using public transportation post on the Lonely Planet message boards. You might benefit from hearing their experience.

Likewise, there are probably people posting on the Rick Steves' message boards who have attempted the itinerary. So long as you understand a lot of them are true-believers in the religion of everything "Rick says," you can probably pick up detailed tips from people who have actually done this themselves.

Good point about the possible slush. I was there towards the end of June, and stayed in a lovely place IN Castelrotto. The lifts were certainly open then, and I could have used some shade.