Mike, there is so many variables to consider on something like this.
They are mainly used here for controlling crappie-but will eat other species...readily. I would strongly error on the light side if it were mine. Predation on the most abundant species present will likely be the result with consideration of size.
This would be a WAG not knowing your system but 5-6 in a pond the size of yours would be as high as I would feel comfortable with not knowing for sure what your goal is.
This is somewhat uncharted area here, so I'm hesitant to say any more would be "ok".
