I've lived in Korea for a few years (mostly Seoul, but also some other places) so I'll chime in too, I'll basically lay it out how rance did.
1. Being NT is generally important, but if you are a tiny bit socially awkward it won't be a huge deal, but you have to make up for it in your looks/status/money. If you really like want to assmilate/date at a high level you need to learn how to read the room, subtle nuances/tells in korean. Koreans are extremely judgemental so if you cannot do that it's 눈치 없다 and a huge failio.
2. Unlike what rance said about japan, I'll say language is not as important. If you want to make friends, social groups, go steady then yeah it's important. For dating however, people will value your looks/height/status/money much much more than how well you can speak korean, if you have none of those things and cannot compete with korean men then knowing korean well will not save you. Notice how the foreigners that girls want to fuck generally aren't the dudes you see speaking fluent korean on korean shows. However, if you are already a chadlite and can pull decently then learning korean will probably improve the quality of what you can get and make dating more fulfilling.
3. Dating apps are generally not good here, I remember there was some statistic where Tinder in korea was like 99% men and 1% women, it's very competitive unless you are chad. Hellotalk is actually the one app that's majority women, so you might have better luck there, but again don't be ugly.
4.It depends on what vibe you can pull off, since you're east asian bar/clubbing or daygame would probably work in your favor.
Since you said you were chinese, there's alot of racism against chinese here but if you can kpop max and you're good looking and tall it won't matter in clubs, literally girls will come up to you. It also should be easy to get foreign girls looking for their kpop oppa over in Hongdae
