Official Web Site for Mt. Fuji Climbing
The most comprehensive but somewhat monotonous official website specifically dedicated for climbing Mt. Fuji and its safety, cooperatively operated by the Ministry of Japan, Shizuoka Prefecture, and Yamanashi Prefecture.
▶︎http://www.fujisan-climb.jp/en/
Understandably, both pros and cons of this inclusive website is that it is official, i.e. bureaucratic: while it provides general information you should know as a visitor, its emphasis lies in security in the mountain and the manners of hikers, and does not necessarily mention real-world details you might be interested in.