Firenze is not a name, although there is the similar-sounding name Fiorenza, which is the Italian form of Florence (the name, not the place). Why not go for that instead? Firenze is just silly.
I can't imagine any Italian person using this name, and it would sound very strange all over Europe, actually. Outside Europe, it just sounds rather foreign and bizarre. So, I can't say I like it as a name for a person.
In the Harry Potter books, Firenze is the name of a centuar who teaches Divination at Hogwarts. The stress is on the second syllable, and the "e" at the end is pronounced: fi-ren-zee.