From some of the research I have seen, expect most crappies to live 6-8 years with some pushing the 12 year mark.
Crappies YOY generally have fairly fast growth rates, making them too large too fast for many larger crappies to eat. Will crappies eat crappies, you bet but they aren't gonna be able to eat enough nor will YOY crappies provide quality forage. Keep in mind though that crappies and the black ones in particular are able to do well on larger zooplankton and no to few vertebrates in their diet. Now larger crappies will struggle to fill their bellies as invertebrates, particularly zooplankton only get so large.
The challenge you have with you pond is your crappies have a huge head start on any other fish you stock. If one wants to have crappies in their pond, I would generally recommend they be added 3-4 years after the bass are added. This allows there to be enough bass of a large enough size to effectively prey on crappies 5"+. With your situation, even if you stocked predators now, it may take them 3 or 4 years before they become effective crappie eaters. That means there may be 3 or 4 more generations of crappies to deal with...
This is far from proven, but here's the route I'd go if you are really trying to grow some quality crappies.
Minimize vegetation and cover/structure in your pond. Stocked 10 pounds of FHM and 10 pounds of the largest GSH you can find. Try to get the GSH in soon as they should be ready to spawn here any day now... This fall I'd then try to source the largest HSB I could find and stock 50 of them. Do not pellet feed the HSB. Hopefully they'll take to feeding on the crappies along with some GSH and FHM no doubt. As they thin out the GSH and FHM, they'll be stuck with mostly YOY crappie to eat.
