Yeah, it depends on the amount of sarcasm in it, and if you use it as a complete noun phrase ("nice guy" being treated as a noun in and of itself) or as an adjective and a noun (a guy who's nice). It's all about context.
Considering Japan, I'm sure they're happy their children get married. It's also cheaper for them to support a couple as opposed to two separate individuals. I missed if her age got mentioned, but he did turn adult. But also yes.
Average male fantasy. I'm not complaining though. Because I also have this fantasy. Having a nice, thankful wife who loves you and your parents must be nice