Itinerary Assistance

Bruges is a small town. A day and a half there is more than enough. You could stay in Amsterdam, a major city with a lot to see? Day tripping uses up a lot of your time, three to four hours each way between Bruges and Amsterdam. The train between Brussels and Florence takes about 18 hours, multiple changes, and costs over $200. You should look into flying.

You might consider visiting places that are closer together, unless these are all your dream stops and you will never be back. The outlier is Florence, as that is very far from the others, and you will pay a lot to fly out of Florence vs. a bigger city like Rome. London is good for four full days at least, as we did earlier this year (we have had several visits previously together and individually). Bruges, I would say two full days is about right (three nights). Florence, three fulls days is about right, but I have always been there when balancing vs. more days elsewhere in Italy, and other cities always beckon. I have not been to Amsterdam, but you might consider that rather than Florence. Also I have been briefly to Brussels and think it's worth a couple of nights and full day. I guess you have probably been to Paris, but that would be another obvious choice. The way flying is these days, I would avoid getting on a plane during your trip; too much hassle and risk or heartache. Except for the flight to and from Europe, of course.

@VS She has a wedding in Florence.

Check a site like Rome2Rio.com to get an idea about travel times and options between the places you have on your current itinerary. If you are willing to eliminate London it would be a more relaxed trip to concentrate on Belgium and Italy.

I don't know how long you need to be in Florence for the wedding. Amsterdam is a wonderful city and deserves at least a couple of days. One day is plenty for Bruges. For me, two days is ample for Florence. I would minimize those two and spend the time in Amsterdam and Rome.

Brugges is a strange choice (I do not say a wrong one, that's up to you). But you could visit Paris or Amsterdam, or spend more time in London or Italy. Is it really what you want to do with your time? And I'd fly to Italy for sure. That time of year I'd probably prefer the south. Rome is a feasible day trip from Florence, about 1-1/2 hour each way by train.

Fwiw, we spent 3 nights in Bruges and wished we could have stayed longer. We loved it.

Easiest way to go from Belgium to Florence is via EasyJet.com from Brussels to Milan. They're the only budget air carrier going into Northern Italy from Belgium. Then the train into Florence is a easy ride.
I checked if Amsterdam had any budget carriers going to Northern Italy, and they don't.

Easyjet has flights from Amsterdam or Brussels to Milan.

One suggestion would be to change your itinerary slightly. Fly into Brussels. From Brussels, it is an easy trip by train to Bruges (take the train from the airport to Brussels Central and then switch to a train to Bruges). The trains are frequent. I started a trip in Bruges a few years back and it is a nice place to get over jet lag. I bought my train ticket on arrival in Brussels. Spend 3 nights in Bruges (2 full days) and then take the train to London (regional train back to Brussels and then Eurostar to London). Spend the middle part of your trip in London and then fly from London to either Florence or Pisa. You should be able to find an inexpensive flight. easyJet has a flight from Gatwick to Pisa, but also look at BA.