Hi,
Sorry to say I can't offer any advice on the Croatia part of the tour as I've never been to that part of the world. However, I've travelled extensively in Italy (Venice, Rome, Tuscany, Amalfi coast) and, as Mark says, it never disappoints. This sounds like a lovely tour and I'm sure that you'll have a great time. Wonderful scenery, architecture and history, not to mention the food and drink! - what's there not to enjoy!
Have a great time and I'd be really interested to read a review on your return.
All the best
Mike