1. food guides. as Josh or somebody else noted in a post, Sandra Gustafson's book, Cheap East in Italy is a useful and generally reliable source of info for chowhounds. It helpfully covered for Rome Venice Florence (thats exactly where we went) and we used it all the time. Faith Willingers and Fred Plotkins books were also helpful, the Gambero Rosso and Osterie in Italia guides much less so for our big city destinations. I was mad at Slowfood for sending me (very expensively, by express mail) the 1999 Osterie book when when I arrived in Italy 1 week later the 2000 book was in the stores. Just plain shoddy.
2. Northern Italy is not very good territory for a vegan. There is generally receptivity toward vegetarians but it dies out when you say "no animal products". Very little but grilled vegetables, spaghetti with tomato sauce (no cheese), boiled greens, bread and some bean and veg soups are available and the soups are often made on the assumption that added cheese will be a major flavor component, so when it is not added, they are bland and boring...
3. I saw a lot of "surgelato" stores, especially in Rome, selling frozen foods, particularly seafood. They were much used. Lots of people were patronizing the frozen food areas of the "supermarkets" too, including in Venice. Surely a dire sign of the times.
4. Our apartment rentals went great in all 3 cities (4 rentals in toto). Internet a super resource for this and rental great for taking advantage of the still abolutely wonderful local markets - my two regrets, not cooking any of the stunning fish from the Rialto fish market, and not having time at the end of the trip to shop for cheeses to bring home (and forgetting to pack the 1kilo of panpepato I did buy!)I will recommend an excellent rental agent when I get around to posting re venice.
5. The Christmas/New Year holidays are a tough time to visit Italy, with all the closing days - I think there were a least 6 when things - except for some restaurants and churches - shut down utterly. Lots of restauranteurs take their vacation then too. Venice and Florence were both freezing cold, V was clear and beautiful (except in the fog, and boy was it chilly in the fog), Florence grayer and wetter. I envied the Italians their fur coats! Rome was definitely in a more moderate climate zone. However, we were told by the Florentines that the weather was never so cold so early, and that at most they got a week that cold...usually in late January... each year. Also, it got dark starting at around 4 (just when things started reopening after the siesta, curtailing touring. Bottom line- there were definite minuses to visiting northern italy in this season - I will aim for a late winter/early spring or mid-fall visit the next time.