Tiger barbs can be nippy and aggressive if not kept in large enough numbers.
Hatchet fish are surface dwellers, so you may need some mid water fish as well, which will cut your numbers down.
Unfortunately Neons do not shoal, per se, unless you startle them, and more often than not they just hang around separately or one picks on all the others and they hide (this is usually a bossy female ) I do not know what Cardinals are like, P44 may be able to elaborate on that.
Pencilfish seem to hang around together more, but swim at an odd angle.
Threadfins are nice, swim fast and in the quantity P44 suggests would look good.
Whatever you do, do not use Neons to cycle your tank, they are not particularly hardy in immature tanks.