V/A- (으)면 and V/A- 다면/는다면

I. 'V/A-(으)면' is general way to say "IF sentence" and can be also used to form conditional sentences, but 다면/-는다면 and N(이)라면 are only used to express "IF sentence" and more hypothetical than plain(으)면. If the assumption is the uncertain/impossible thing in reality, both -(으)면 and -다면/는다면 can be used but -다면/는다면 is more natural than -(으)면because we use more -다면/는다면 than (으)면 when the assumption is somewhat impossible to happen. So when the reality is the complete opposite, You ought to use more -다면/는다면 than -(으)면..

① (너 한국에 가니까 )한국에 가면(O)/간다면(X) 한국어 사전 사 와.
When you go to Korea, get me a Korean-dictionary ( because you go to Korea)
(The listener will go to Korea (possible to happen) and this sentence is used as
conditional sentence, so 다면/는다면 can't be used.)

② (이번에 한국에 못 가) 한국에 가면(?)/간다면 뭐 할 거예요?
(I can't go to Korea.) If I go to Korea, what will you do?

③ (너 내일 한국에 간다면서?) 한국에 가면/간다면(X) 뭐 할 거예요?
(I heard you're off to Korea.) If you go to Korea, what will you do?

④
A: 인생은 불공평해. Life isn't fair.
B:내가 너라면/너면(?) 그렇게는 생각 안 해. If I am you, I don't think so..

II. Also, -다면/는다면 can be used when the speaker speaks out how he/she thinks about quoting. but it implies the events which have little or no change of actually occurring...
⑤
A: 나 한국어 공부해. I am studying Korean.
B:니가 한국어 공부한다면 누가 그걸 믿어? If you are studying Korean , who can believe that?
니가 한국어 공부한다면 나도 그렇게 할 게. If you are studying Korean, I will do so, too.