@Cycloptichorn,
What a happy decision!
I've only been to Italy, several times totaling 2.5 months - but I read a lot about travel of many kinds. It's a way of travelling vicariously.
I've lots of opinions, which naturally are based on my reactions, and may not make sense to anyone else.
Two weeks is shorter than you think, especially flying from California (which is where I flew from, and so does CalamityJane). Jet lag to start with when you get there.
I wouldn't do four major cities in two weeks, even though I'm very keen on cities and like to walk them. I'd pick two (possibly a third) perhaps landing at one and flying back from another, if you can work that out, and in between, either train or car to a third area, to sample a smaller city/towns and country surroundings.
I like to go in Spring or Fall, missing a whole lot of tourists and saving scads of money.
On planning -
On our first trip, we took a month and only reserved a hotel for Rome, Venice, and Florence. Stayed in Rome at the beginning and end of the trip something like 9 days total (the hotel kept one of our too big suitcases for us), took the train to Venice and again to Florence, then rented a car for a week or more driving around Tuscany stopping where and when we felt like it.
Second trip took two weeks, Rome again, taking trains to places that attracted us from reading up, and back to Rome. This one was slightly more planned out.
Third trip, I went to do photography of piazzas, took a month, went to thirteen cities, mostly not too large, Rome again to start and finish, almost always trains for the twelve other cities, except for one bus. This trip was intensely planned. Because of the number of places and importance of time, I knew every place I was going to stay except for two cities, Faenza and Ivrea. This was just prior to my knowing how to google, so chose by travel books and made reservations by (will you believe it?) fax or telephone.
Many cities and towns have tourist information places - and I've used them a few times to good avail (e.g., Faenza).
On my last trip, I ended up not liking Ivrea and therefore got to Florence two days before my reserved time there, with no room available early at the place I reserved at. In the train station, there's a tourist office. I looked at the available hotel room list, and saw, amazingly, the name of one I wanted to stay at in my planning stage but was way over my price range. There was a room there for something like 35% of what I saw before on published lists. Yes! It was small but otherwise perfect room in a perfect place.
Packing varies - we took way too much for that first month trip, but we didn't know any better. Packed much lighter for the second. The third, for a month, I took a duffle bag and a big purse. (There are ways to pack that light.) A few times, I went to a post office and sent some stuff home - art books I couldn't resist, etc.) Duffle bag? I like to be able to control what I am carrying, so like it better than a big backpack. I take a lot of trains, and don't like to go down a huge number of steps carrying a bag with wheelies - those are heavy.
So, if you are going to nice hotels by taxi, load up. If you are going to be walking with your bags, think efficient packing.