Wang's flat is the place to be except if you have heavy luggage :) there is no elevator so you'll have to climb 3 floors.
The flat is very well situated. Uffizi gallery and Palazzo Vecchio just around the corner. Ponte Vecchio 2 min walk. The Cathedral 5 min walk! All you need to see in Florence is next to you even the train station can be reach by foot (20 min walk). And Wang is such a nice person, very kind and discrete!