You literally have cities in China that are called "second wife villages"(二奶村) where politicians and rich people have their mistresses that are located close to ports/airports for quick access on "work trips". In Shenzhen for example its the Luohu (罗湖) and Futian (福田) districts that are for this purpose.
Correct, and OCT (also in Shenzhen)
Might be but last time I checked Huang was not Chinese.
It's a bit much to say the purpose of Luohu is mistresses, but you're right that it definitely is not a Japanese-specific thing.