I spent two weeks in Italy for my honeymoon.
Milan isn't a good tourist destination. Amalfi is great but it's too cold for that.
Venice is fine but I wouldn't recommend staying there for more than a couple days and one night just so you can see a few of the things. The gondola rides are a huge rip off (Like $100 a half hour to ride in a fucking boat)
Firenze is an italian paradise and I'd recommend staying there for several days.
You'll need to spend at least 4 days in Roma to see everything that you need to see.
My recommendation is find somewhere scenic to spend 4-5 days in and think of that as your 'honeymoon' and spend the rest of the time being a tourist seeing Italian churches and art.
fuck it I'll just start copy pasting shit from my spreadsheet we made before our honeymoon:
rome:
vatican: spend an entire day here
Collesium/forum/palatine hill Here's a tip: you can avoid the hour+ wait in line for a ticket by buying one at the entrance to the Palatine, inside the Imperial Fora. Then, you can enjoy feeling smug as you bypass everyone who didn't know this!
pantheon: must see
spanish steps/trevi fountain: must see, watch for gypsies and pickpockets
trastavere: Go here for dinner/drinks/night out, it's the most happening place after dark
cappuchin crypt: Crypt of 4000 monk skeletons whose remains are arranged in decoration lol
Borghese Gardens: best outdoor area in rome.
http://www.anticabirreriaperoni.net/If you enjoy pubs go here, it's a german/italian style pub. Have your wife order the kilometer
firenze:
I'd recommend taking one of the tour bus rides in firenze that goes up to fiesole
http://www.firenze.city-sightseeing.it/eng/#
Galleria dell'Accademia: Has michaelangelo's david, huge line get here early
Uffizi Gallery: must see,, get here before it opens
We stayed at
http://www.florence-youth-hostel.com/and really loved it. The other places we stayed at were ok but we'd recommend this one strongly if you're ok with a hostel.
venezia:
The only remarkable thing in venezia for me was the seafood and
http://en.wikipedia.org/wiki/St_Mark's_Basilicawhich has the incredible
http://en.wikipedia.org/wiki/Pala_d'Oro
It's also extremely difficult to navigate venezia so get your lguk and sebilis skills ready.