the original theory was that it would be pretty self sufficient, as it would have similar stocking and size to many of the ponds and lakes near my house, with mostly the same species. We wanted to keep mostly natives, plus some koi. I figured that adding a few texas cichlids and high fin sharks (for a total of about 12 non native fish) and a bunch of native fish would be a pretty stable environment.
The other option i have considered is making a stream to the main pond, possibly with a a smaller pond part way upstream. However, if i were to do that, i would probably want the pump to be solar powered - is that possible?