Any lepomis species will be to agressive. Stay with the smaller minnows, dartes, and the like. Madtoms would be perfect for this tank, just don't expect to see them an awful lot. As per your original suggestion, I would leave out that many yellows, or leave them out completely. Theoretically, pumpkinseeds can get to a max of 16" or even possibly larger. However, there are usually limiting factors in a fish tank that don't allow them to reach that size. The point was more that they have that potential. Also, I've handled a 24" crappie. Most everybody is gonna cry balloney on this one, but i don't care, I know what I caught.