The scaffolding for the renovation is not due to go up until April. They will start moving some of the construction materials onto the castle grounds in October so you may see some of that activity but the castle itself will still be open and definitely worth a visit.

In my experience, mid-October in Japan will still be warm and fine with occasional rain showers. The last time I was in Tokyo in early November I was in short shirt sleeves 5 out of 7 days. I had similar experience in western Honshu last year in October. Very pleasant. Only put on a light jacket in the evenings and got rained on twice in 10 days.

J.R.