My husband and I stayed one week at Mizunagian, and will definitely come back next time. The house is beautiful, and the location is very quiet, while also being in a very central location. We loved the view of the river, and the traditional soaking tub.
The house would be comfortable for 4. The stairs might be difficult for small children or elderly adults, but we plan to come back with our children next time.
Toshiua-San was a great host and very responsive. Highly recommended!