Thanks for the fine review.
Haven't seen the film yet, but I'd like to recommend a similar film from Shindo he shot some years later: Yabu no naka no kuroneko "Kuroneko / The Black Cat" which is an outstanding film for transcending it's simple story and the horror formula into an existential piece of cinema. Expressionistic and surreal, this could probably make a good double-feature with "Onibaba".