I wouldn't worry about eating carp because of the "junk" they eat. They eat the same crayfish, insects, and stuff that most fish eat, including walleye.
But if you are going to stock a pond with Koi (which are pretty much carp or goldfish which aren't carp but I beleive related to carp) for eating, I would just stock carp, catfish, drum, suckers, or buffalo.
