Some people will tell you they are good in a 80L, in 4-6 family.
For me, in a 100L tank, I'll definately go with smaller fish and a larger shoal, much better looking. Remember, like most Autralo-Guinea fish, they are really very very good and fast swimmers. I think 120-150cm is a minimum and a large 10-15 shoal to have your eyes plenty. 6 fishes will give you 2 males and 4 females, It could cause too much harassement between the only 2 males, stress, not the true behaviour... The males battles are impreesingly beautiful, they run one behind the other in a circle shape, head-to-tail of each other.
Then, each person maintains the fish as it likes, but not always in the best conditions, sadely