Sounds like a wonderful trip, and this is just my personal opinion, but I'd suggest more time in Venice and Florence ( and perhaps a trip to either Verona or Pisa from Florence) and cut out Milan and Zurich altogether.
Venice is a "hub" airport, and you could end your Italian leg there and get a flight to Paris.
You could get a train from Venice to Paris, but for details, I'd suggest posting in the rail travel forum here on trip adviser.
The advantage of rail over internal flights is, there are no luggage allowances restrictions on trains. Flights, especially low cost carriers, impose strict luggage allowances and the fee's for heavier and/or extra bags can really push up the price of LCC flights.
For up to date information about accommodation ( and restaurants/guided walks/itinereries) ,I'd suggets reading the information and reviews for your destinations in the specific travel forums. I've found that the JBR's ( just back reviews) from other travellers to be particularly helpful, as well as a good read!
Generally, B & B's are cheaper than hotels, but as this is a once in a lifetime trip, you may want the odd "spurge" hotel. Hotels belonging to the main chains tend to offer consistent quality, but may be a bit lacking in individuality. It may also be worth checking the "speciality lodgings" in the destination forums, as you can uncover some real gems there. .
Venice has lots of accommodation for all budgets, some of which could be on the beaches of the Lido, as well as nearer the main railway station, which is less expensive but very fast and easy to travel to the Grand Canal.
Please bear in mind that the "star" ratings that hotels use, are not always a good guide for quality, as the ratings are awarded by the local tourist board. There isn't an international agreed standard for star ratings, and having once stayed in an awful 3 star hotel in Paris, I now research as much about the hotels as the destinations.
Edited: 4:52 am, November 11, 2012