I've ridden in Italy or France most years since 1995. The Sella Ronda is my favourite ride, the Stelvio my favourite climb. I'm returning this year for a week in Corvara, another six days moving around, including Bormio. This will be my sixth time in Corvara, third at Hotel la Perla, the best place in town with great food and service. When we were there last year, so was Miguel Indurain, who rode the Maratona with his son. I rode it with my son but we weren't special guests, just regular guests who had a good time.
Fly in to Venice, ride Monte Grappa, then go up to the Dolomites. Corvara, Canazei or Arraba offer lots of routes in their areas and are all pretty close to one another. Sella Ronda, Marmolada, Falzarego, Giau,etc. Yes, the towns are touristy but that also means that there are lots of hotels at various price levels and lots of places to eat. If you're in Corvara, there's a good bike shop in la Villa, about 5 km down the hill. Bike shops are few and far between in the Dolomites in my experience so it's nice to know there's at least one good one.
Cortina is also a good location but I find it a lot more expensive than Corvara. I'd suggest a week or so in the Corvara area, then drive over to Bormio for a few days. Three big name climbs in that area - Stelvio, Gavia and Mortirolo. Lots of good hotels in Bormio, some of which cater to cyclists in the summer. Like Corvara, it's mainly a ski resort. You could then drive from there over to Como and do Ghisallo if you want and fly out of Milan if you can organize car rental and flights that way. If not, take the autostrada back to Venice.
Buy a Michelin or similarly detailed map of the area (you probably will need two to cover the whole area). Go to this site to look at the profile of the climbs:http://www.zanibike.net/motore.aspx?lingua=eng
Have fun! Great biking and good food.