Keep every crappie you catch is a good start. You can really hammer them in the early spring when they are on the spawn and just after.

Fyke nets are a very effective removal technique for crappies. If you have a second hand to help in set up and removal they are ideal. The nice thing about them is you can control exactly what they do and don't remove as you can release any fish you want and keep those you do. They also help in monitoring other fish populations. For any pond owner, they would be high on the list for purchases IMO.

Many fish species eat fish eggs, but crappies lay a lot of eggs so thinking fish will control crappies by eating eggs is a major stretch. HSB have been shown to be a possible effective predator on crappies, but the studies showing it are very preliminary at best. In me experience, a healthy LMB population with a decent number of mid sized bass seems to be the most effective control. You want to bass to eat many of the crappies in the 1"-4" range before they became the over populated 6" paper thin mess.