For this trip, considering the fact that you need to fly out of Vienna, I'd keep close to the Geography of the original plan. More of Austria. Do NOT ruin your trip by trying to "do it all" in this one trip! As much as it breaks my heart to say this, don't go to Italy. Spend at least 3 or 4 nights in each location, so that you don't spend your entire honeymoon looking at Europe from te window of a train or bus. Drink in the beauty of the cities on your original itinerary, and enjoy yourselves, and relax. The next trip can be for Italy.
Every time you change cities, you will lose a half day of your precious honeymoon time: check out of hotel, taxi/bus to train, ride train, bus or train to next hotel, check in. Get situated, etc...... Remember Arrival Day and Departure day do NOT count, as the day you arrive from an over the Atlantic trip you will be jet-lagged, and will just need to explore the area around your hotel and get on the European time clock. The day of departure (if going directly back to the US) you will not do anything except get up early, pack, and get to the airport! So, while it seems you have a very generous amount of time, subtract those travel days, and subtract the days you will be changing locations, and it's not quite as long as you had originally thought.
I don't know what your itinerary is, but add a few days here and there to each city you're visiting, They're all amazing. Go to Italy next time! Congratulations on your wedding!!! Now, relax.