I'm heading to Europe in May, with a similar travel itinerary.
Fly to London. Stay at Hilton London Hyde Park for five nights.
Fly to Rome. Stay at H10 Roma Citta for four nights.
Train to Florence. Stay at Hotel Davanzati for four nights.
Train to Venice. Stay at Hotel Panorama in Lido.
Fly to Paris. Stay in an apartment rental for five nights. Check them out here:
http://lovingapartments.com/Paris-apartments-home.html
Fly home.
I wanted to go to Cinque Terre in Italy, but they had a big mudslide in November 2011. It should be fine when you're there, but do some research first.