MN, if those black crappies are up to 5 inches long now, they may be able to spawn next spring. Generally speaking, crappies mature at about 6-7 inches or so. So, if they still grow some this fall, they might be capable of spawning next May or June. So, I'd sure want a predator in the pond with the crappies to try to control their offspring. Does your dealer have any advanced fingerlings of largemouth bass or walleye? I'd prefer largemouth bass, as I said earlier, but at least the walleyes would be a predator. This is one of the problems with various panfish species -- they often mature before the predators, especially this far north. Largemouth bass don't mature until 11-12 inches, while the walleyes don't mature until 15-17 inches. If the crappie spawn is uncontrolled, then the crappies will overpopulate and stunt, and you won't be happy with their small size.
