Definitely looks like too much for 8 nights.

Naoshima (and the surrounding islands) needs min two nights, if you want to see all the art, museums, etc. Teshima Art Museum on Teshima island is a must see and there is a special night exhibit at the Chichu Art Museum that only shows on Fri and Saturdays. It will take some planning if you are on a tight schedule as the small ferries between the islands don't run very frequently.

If you can't afford spending 2 nights in/around Naoshima, I'd cut it from your itinerary.