Pencilfish care

Yes.

Especially as, depending on the species, sometimes males can become territorial and it may not work to add more males later on down the road.

isn't a shoal just a grouping of fish that hang together for whatever reason (safety, food collection, etc). they don't even necessarily have to be the same species. there is no distinction of male/female ratios. but just like most other small fish, pencilfish will do better in a shoal, which includes being more active, showing more colors, etc.