First of all, I urge you to pack lightly--Rick Steve's website has good packing lists. You'll have lots more fun if you don't have a lot of luggage to lug around. No one cares if you wear the same clothes over and over again. So, now, you'll fit into something like a Citroen C-3 (a really fun car to drive), or, at most, if you really have to splurge, a Ford Focus wagon or similar. After much research, we've always found Hertz to be cheapest, booked through the AAA auto club. On the car rental websites, they have suitcase icons that will show you how many, what size suitcases will fit it each car. But you can go to the AAA office, and they'll do the whole thing for you. A Red Michelin guide will come in very handy, because they have maps for each city, which will give you a clue as to how to get into the city and find your hotel. Also, if you decide to go off your plan (really, at this time of year, you could do the whole trip without reservations), you'll have lots of hotels to choose from, that you could call in advance, as you near the next destination. I urge you to have a cell phone. And walkie talkies for everyone.