concur...dont' miss Florence...but, be sure to drink too much chianti. Buy gold and leather at the Ponte Vecchio and San Lorenzo & Nuovo (be sure to rub the boar's nose) marketplaces.
You don't really need a tour if you find a good travel agent that can work out your itinerary. Stay at hotels with english speaking concierges to make dinner reservations, arrange taxis, etc...I did the backpack thing without speaking a lick of "eye-talian"! You just have to stumble thru it it and laugh a lot.
Venice is a tourist trap....Rome is a big, dirty city....they both have their charm and are places to go before you die.
You are going to have a great trip!