It's a small space, but for a Tokyo location you can't ask for much.
We stayed as 4, I would say it would be comfortable for 3.
Host responded in anywhere from 0.5 to 4 hours after messaging on AirBnB. You do get an automated message immediately but it won't address every concern.
The place itself was well kept and had all the listed amenities. I suspect the other neighbors were also tourists as they could be heard partying it up. Not enough noise bled through the walls to prevent us from sleeping, but if you're a light sleeper it would be something to consider.