My boyfriend and I had our second stay in Nakano at Toshi's apartment and stayed for a week. I wouldn't recommend being more than two people here, seeing as it is quite a small room. Overall the apartment was clean and had everything we needed for the week. However, since the apartment is on the bottom floor there is a lot of noise coming from the outside, and quite a strong draft through the front door. The AC helps but it can still get quite cold (we stayed here in march) especially in the mornings.
Toshi was quick to answer any messages and Nakano is a Wonderfull part of Tokyo to stay in, far enough removed from the busy night life to get a good nights sleep but close enough that you can travel within the city easily.