A Crappie will be like any other fish and eat the largest fish it can. If you stocked a 2-3" Crappie, it would eat lots of FHM and juvenile GSH until it gets around 6", which would happen quickly. Then it will all but ignore FHM and small GSH.

To help you put things in perspective, a "Gallon" of GSH is ~8 pounds of fish and will reproduce, probably over 100 hundreds pounds a year after YOY grow. ONE Crappie probably won't eat much more than about 10-20 pounds in an entire year.