We stayed in Paolo's apartment with three girls for a weekend and had a great time.
First of all, the location is amazing! Located in a cute backyard you're still absolutely central without any noise. The walk to P.ta Genova is 5-10min but there are plenty of Gelato shops in between if you want to take a break ;) There is a cute breakfast place called Felix at the end of the street where we literally went every day.

The apartment is tiny but cute. I'd say it's perfect for two, alright for three and it would have been quite cozy with a fourth person.
There is a couch on the ground floor for the 3rd/4th person, which is surprisingly comfortable. It would have been nice if the couch would have already been prepared for the third person, but we found everything we needed in a box next to it, so it was alright.
I'd definitely recommend staying there and will come back the next time I'm in Milan.
Thanks for having us, Paolo!