Bill,
Thanks very much for the info. I believe that I will go ahead and get the eelgrass from the river. Basically because of availability and economics (translated: easy to get and free \:D ). I especially like the prospect of having some minnows in my pond again. I like to watch them swim around.
I will probably only plant the shelf that I described. Then if the eelgrass ever becomes a problem, I will stock some amur. Although from your information, I really don't think that there will be any problems.

Thanks again,
Larry