I'm personally in favor of picking a city and staying there for a week, but that's my travel style. I wouldn't be good at giving any advice on how to do a road trip in Italy - I've personally never done it. Our first trip there we did Rome, Florence, Venice in 12 days and I personally found that pace to be a little too high - we saw the major tourist sites, but that's it. Now we pick a city, get an apartment or a hotel some light services, and make that home base for a week or two.