9 days in Northern Italy

There's no such thing as a generic ideal itinerary. It depends on your personal interests, and even then there would be many really good itineraries, not necessarily a single one that was obviously the best.

To the list of possibilities you already have, you might add Padua, Vicenza, Ferrara and Torino. Your interest in Milan suggests a possible preference for urban areas, which might make Torino also a good choice. I haven't been there, but the folks who have been to both Milan and Torino (not that many people, I admit) all seem to prefer Torino.

The great, non-lake destinations in northern Italy constitute far more than nine days' worth of sights, so I think I might make logistics a major determinant on this trip and plan to return later to hit some of the places I missed. Venice, Padua, Vicenza, Verona and Milan are laid out nicely right along a major rail line. You could do worse. If you need more, you could extend to Torino or side-trip to Ferrara, as little as 30 minutes from Padua.

The above should not be taken as discouraging the other nearby cities and towns. I liked Bologna a great deal (more than Milan, but I admit the Duomo is fabulous), and Ravenna is just beautiful even before you start visiting the mosaic sites. But with just nine days (and I see that you're counting Day 1, which I do not since I am always a zombie that day), I don't see much sense in zipping all over the place, leaving great places unexplored in your wake.

I enjoyed Milan, despite the lack of attention. In one full day I got the the roof of the Duomo (getting there first thing- 9ish maybe?) to go up, then seeing the museum and cathedral itself, then to a couple of the churches in the RS book (well worth the time if you like art), the Pinocateca, Sforza Palazzo (briefly, mostly to see the Michelangelo Pieta), and finally the Last Supper at night. It's a long day, but workable as Milan is easy to get around. I also saw an opera at La Scala the first night in, and one other museum another night after the World Expo. Summary is that 2 full days will let you see quite a bit of the main sites, and spread out the time a bit. With a third day, you could do shopping (or window shopping) if that's your thing, or see some of the other neighborhoods that seemed really interesting. I'd give it two full days (three night) minimum since you like cities. Probably the same for Venice, and maybe a third if you wanted to go to the islands of Murano/Burano/Torcello. Or plan on one full day for the city and one for the islands? Venice itself is more interesting and filling two days just there will be easy without having to go anywhere.

Mantua has a couple of really nice Gonzaga palaces, and the center of town is not all that large so nice to walk around. They have really nice collections of art. If weather is good, you can rent a bike and ride around the lake if the art is getting to be too much. Parma also has a nice center and good food, although Mantua might provide a better contrast to the other two cities.

Given your time, three cities would be a comfortable pace. Four if you want to cut back on you main cities and throw something else in. (I'd vote three. You could always day trip to somewhere from Milan or Venice if you felt the need).

You mention that you enjoy historical sites and art. If that includes the performing arts, would you enjoy art performed at a historical site? Would you enjoy an Italian opera at the arena in Verona?

Even if you don't think you do/would enjoy opera, if you are there during the arena's (summer) performance season, you might consider seeing Aida ….or another performance. I never considered myself to be a fan of opera, but I've found during my travels that the right opera in the right venue can be magical. There is something truly special about Aida on a (nearly) 2000 year old stage in Verona! The production is magnificent! Bring a cushion ….the 2000 year old seats are not velvet and cushy :-)

If that interests you, then check their calendar and plan your itinerary to stop in Verona for a not-to-be-forgotten performance under the stars!

Verona is one of my favorites. Venice is my second favorite city in the world. I liked Bologna, loved Ravenna, haven't been to the others you mentioned. I'd choose only one other place besides Venice and Milan. If you like fast-paced trips you could squeeze in one more.

If you want to cram in more, spend a day in Verona between Milan and Venice (luggage storage at the train station). Then stay in Bologna and day trip to Ravenna. Both Verona and Ravenna are worth 1-2 nights, but you don't have that much time.

Rick has little to say about Bologna, so read a different guide book and make a personal short list. Bologna works for a sleep spot between Milan and Venice with plenty of day trips from there after viewing the city itself. If architecture is also of interest, then consider that Vincenza and environs have many Palladian villas to visit.
I think you really need to check,out some guide books (DK Eyewitness are very pictoral, but heavy for travel, so get them from the library), and watch YouTube of some of the names towns.
If you like cars, Lambourgini is made in Bologna area as are many other famous cars. You might be able to visit factories to do some driving.

Thanks for all of your replies! This is a lot to chew on. One question. Should Milan be at beginning and end of trip, or only the end (with an immediate train to another destination such as Venice or Bologna).

Thanks!

My preference - a necessity if I have an early morning return flight - is to be back in my city of departure at least 1 night ahead. If I plan to sightsee there, I prefer to do it at the end of my trip.

Since you're arriving early in the morning, if you take an immediate train, you avoid one extra hotel change in Milan. Depending on how well you handle jet-lag, a train ride may also be easier than a day of sightseeing.