We had a great time at Lorenzo's place. The apartment is as described and looks exactly the same as the pictures. The location is fairly central and we were able to walk to everything with no problem. There is also a metro stop just down the road. The pizza place right outside the building is also amazing. I would say the colosseum is a little further than 40 m though :)
Lorenzo is awesome himself. He took the time to meet with us and showed us on a map where to go and how to get there. Very friendly guy. He even left breakfast for us!