Kay,
I am not really qualified to answer your question, but since you have had no reply I will try to help. Here are a couple of web sites that contain fish pond management info.
http://www.bagelhole.org/article.php/Water/108/

http://www.dgif.state.va.us/fishing/Pond_Management/index.html

If it were my pond and it was overpopulated with large chubs, I would kill them with rotenone before I stocked anything else. Please note that I am not telling you to do this. It's just what I would do.

Larry