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.
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.
Correct, and OCT (also in Shenzhen)
Might be but last time I checked Huang was not Chinese.