It is -고는 하다 or -곤 하다, not -군 하다. - 옛날에 일본 식당에서 저녁을 먹곤 했어요. GOOD - 친구들이랑 노래방에 가곤 했어요 . (군 -> 곤) - 큰 꿈에 갖군 했어요. => 큰 꿈을 갖곤 했어요 (에 -> 을, because it's an object of 갖다) (You could also say 저는 옛날에 / 예전에 꿈이 컸어요)

I can not read Korean. I can look at the English and talk about it. The first sentence needs an "a" before "Japanese". The second sentence.... I don't think of Karaoke as something you can"go" to. It would sound better to say; I used to go and sing Karaoke with my friends. or I used to enjoy Karaoke with my friends. The third sentence does not sound correct. It would sound better to say... I had a big dream. or I have had a big dream. or if the sentence is supposed to be about a hope for a better life, a goal to strive for, you could say... I used to dream of... Months ago I had dreamt of...... I had dreamed of.....