First, let me thank all the wonderful posters who helped us navigate our trip to Italy over the last three weeks. It was a trip of a lifetime, and your help in planning and execution of our itinerary was invaluable. As a way of paying it forward, I wanted the "newbie traveler" to have some of our thoughts as we returned home.
1) Trains are easy. We promise. We never needed an advance ticket, we bought some at kiosks, and some on the Internet. Regional trains are cheap, reliable and easy to use. High speed trains are slightly nicer and have reserved seating, and also seem to have a lot of A/C--but are more expensive. In 3 weeks, we used only 3 high speed trains, the rest were regionals.
2) Italians are wonderfully patient people, most spoke English to some extent, or were willing to find someone to help us. They spoke much more English than we did Italian. We quickly learned some phrases to get us through the trip, including the phrase to ask for your check in a restaurant, because if you don't ask for it, they aren't going to bring it!
3) Yes, you really can drive through Tuscany and the Hill Country quite easily. We spent a week doing it. GPS worked well virtually everywhere. We had 1 ATT plan and one Verizon plan on separate phones--both worked well, but the Verizon version of Google Maps was flawless.
4) Rick Steve's guidelines on food costs were right on target. We ate a very small breakfast, a sandwich for lunch, a snack in the afternoon, and dinner. We often picnicked, and had great fresh fruit and vegetables in all locations. We found many of Rick's suggestions on low cost sandwich places to be fabulous, and close to major attractions. We became very aware that all you had to do was walk 1-2 blocks over from a major attraction and the food would be excellent and inexpensive--unlike the food on the same road as the big "thing" you went to see. This was consistently true throughout all of the big cities we visited.
5) Our best memories of this trip are "off the beaten path" experiences. We were pleased to see the big sights (although Pisa in 100 degrees with a zillion people was not that memorable...) Don't schedule yourselves so tightly that you cannot enjoy those little experiences.
6) Tours of major sights. We planned and executed our trip ourselves. However, we booked two tours--one in Rome to see the Vatican with early access (expensive and 100% worth it) The tour guide was excellent. The second we booked in Milan to see the Last Supper (tickets were hard to come by otherwise) and the tour guide was mediocre. (We did get to see the Last Supper, and it was incredible.) We should have done the same in Florence for the Duomo and Baptistry--I think we would have gotten more out of the visit there.
Best of luck planning your trip, and do not hesitate to ask the pros on this website for their advice. They are accurate, quick and efficient with their advice. They may not always agree with one another, but their varying perspectives are valuable to planning.