Definitely a good idea to harvest every crappie you catch. Numbers-wise on the HSB, I haven't stocked them myself previously but am going to soon in one of the ponds I work with; I would think twenty to thirty 8" or better would be enough. Don't stock them smaller than that or they'll just get munched by the bass.
What Ric said is right on about the crappie taking forage from the bass - almost certainly that's at least part of the problem. It may be a big part of it. The more you can thin out the crappie, the better your bass are going to do.
If bass are the main goal, you could also think about stocking threadfin shad. I don't know how they do in OH, if that's above their range; if they'll live even in the warm months, they'll help pack on the pounds for your bass.
