This is a beautiful converted palace. Lots of stairs - the ones inside the apartment are very narrow. Although there is sleeping space for 12, the final bed is in the common space, and the common space isn't that great. It would be better for 10. Beds comfortable. Location is a bit further away from the tourist attractions than I had thought - right against the major half ring road, but it was a straightforward 15 minute walk to the major sights.
There is a clothes washer but no dryer. For much of our stay the washer didn't work plus the lower level faucets/showers had no cold water, only very hot. It turns out this was indeed all related, and Federico who lives in the adjacent apartment was very responsive and got the plumber there after which all was good.
Watch out for the mosquitoes in Florence and Venice! Apparently in the winter they come inside and several of us were tortured at night! Bring repellent.