Hi Nanako, I think 3 is the clearest. To me, it sounds better like this: We all have something we'd like to do someday but don't have the courage to do.

Hi Nanako all are good and perfect English. 1, 2 and 4 are most common. 1 is better than 2, because adding "to do' at the end adds emphasis to the word 'courage'. The difference between some day and someday, I get confused with as a native speaker, but I think is best as 2 words. 3. is very good because you don't say "he" but rather "we". It is more inclusive, and neutral. It is actually better English. Daring, courage and 'taking the plunge' are similar, so don't worry if you use one word, and someone else uses the other words. "Taking the plunge" is more involved, as you immerse or plunge into something. Daring and courage can mean the same as plunging, but with less commitment. Overall, your English is excellent, and all 4 statements are perfect, and common.