Joshua's house has been completely renovated and has plenty of rooms. We were 7 people and we didn't feel it as everybody can have its own place. The beds and pillow are really comfortable and it's very important after spending a day walking in the streets of Firenze! However, there are mosquitos in the surroundings and even though the house is fully protected with mosquito screens, it happened some of them made their way in the bedrooms.
Joshua has been a super host, very friendly and responding. He gave us one card to park our car in a public garage and we kept the other one in street parking (18 € per day) in blue painted places.
The appartment is accessible by car which is nice as driving downtown is tricky, the counterpart is that the place is not fully central but accessible with 20 mins walking or with the tram+10 mins walking. In my opinion, it's a good trade off.
Besides visiting Firenze, don't forget to have a one day trip to Sienna which is gorgous and not as crowdy as Firenze!