Hey! We're on the Rick Steves Europe Travel Forum. I would feel remiss if I didn't suggest taking a look at his tour offerings. You may find one that would be a great fit.
Now that I've recommended them, I have to offer full disclosure. We have not taken an RS tour and we almost always plan our own tours. We have taken two tours, but they were under extraordinary circumstances. The first tour was when my wife and I were in high school and we spent 22 days on the "grand tour" of Europe back in 1966. It was a wonderful experience for us teenagers and it sparked a lifelong love of Europe.
The other time we went on a tour was with our dear friends. He is the son of my wife's Science teacher and my best friend in high school. We took a Viking River Cruise down the Rhine exactly 50 years after our first trip! Our friends invited us to join them, we would not have chosen a tour and actually went to Italy on our own 6 months before the cruise.
The advantages of a tour, as mentioned, is all the logistics are taken care of for you. You have to do little more than just show up. Good guides will enrich your experience and give you an appreciation of the wonderful places you visit. You get some free time, but tours have to strike a balance. Too little free time and you feel constrained. Too much free time and you wonder what you are paying for.
Choose the course of action best suited to your personality. Some folks are more comfortable, especially the first time traveling to Europe or a specific country, with taking a tour. If you use Rick Steves, who does tours differently, I'm sure you'll have a wonderful time. If you are more adventurous, find planning half the fun and are flexible and easygoing, planning your own trip is the way to go. It can be a lot cheaper. Our trip to Tuscany was a third of the cost of the VRC for the same amount of time.
If you choose to plan your own trip, don't move too often. With two weeks I'd consider flying into Rome, do three days there, then rent a car and stay at an agriturismo near Siena or Florence for at least five days. Then, either stay in Florence and fly out of there, or stay in Padua and fly out of Venice. I recommend staying in Padua instead of Venice because it is much cheaper and Venice is only a 30 minute train ride away. There's lots to explore in and near Padua.