I keep halfbeaks and mine are larger than 2"-3". I have not noticed that they are "fin-nippers". They are very intolerant to changes in water chemistry and low oxygen levels. Keeping them is not recommended for the beginner. They relish live foods, like guppies. Mine, generally, are topwater swimmers and I don't think I have ever seen them near the bottom of the tank. I have seen them assume an ambush position in the plants in the upper mid-lvel of their tanks. They thrive in a brackish environment with a little salt added to the tank. Mollies, large mollies, would make good tankmates and the moolies babies would provide an added food source. Halfbeaks are also known to be a fairly good jumper, so a full tank cover is a must.
Cories will not work as tankmates because of the brackish water.