I've been to Italy like seven times no joke. Stop by Lucca if you can that city is beautiful as hell also the Cinque Terre is an amazing walk you'll remember for the rest of your life if you take the time. Italy is most beautiful during summer though why are you going there now!
Also Venice is pretty cool, but be prepared for tiny and old fashioned hotels that cost a shitload. Also try feeding the pidgeons it is great fun.
When in Rome be sure to check out the pantheon and the ruins that lie close to the Colosseum. Also drop by the sixtine chapel in the Vatican. If you can go to Milano and go to the top of the dome. That's also one of the best experiences you can have while vacating in Italy.
All things considered I doubt there are many tourists there at this time of year so you'll likely be free to do all those things without a hassle.
But these three things you really have to do:
1. Visit Lucca/Luca, and stay for a day or two. Try walking on the city walls or just sit there drinking red wine and eating olives (this works best during summer, but is probably still fun).
2. Do the cinque terre hillside walk. As I said, it's amazing, and it's pretty much a coastal hill walk where you'll walk through four (or was it five?) villages that are all among the most beautiful villages ever.
3. Got to the top of either the dome in Milano or the Vatican. Both are amazing walks and really makes you feel alive, especially after the 300 or so steps to the top. I've done this quite a few times already and it's really worth it every time.
So yeah my dad is a sucker for Italy so we go there a lot. If you intend to visit Lucca or the Cinque Terre be prepared for not many people speaking English as opposed to Rome or Venice. In Lucca we couldn't find a single person that spoke English but I'm pretty sure they're there, especially since it's becoming increasingly popular as a tourist destination (although still underground).
Other than that...uh... venice is most definitely not beautiful, it just stinks absolutely horribly. The majority of italy is so very good but venice is awful.
I thought Venice was pretty cool since it's pretty much 17th century houses on a shitload of water and there's fucking bridges and boats EVERYWHERE. It's a really unique city but yeah it's a bit filthy but overall I thought it was rather great. Also the war museum is p. cool.