I can't imagine having a large enough population of frogs and insects to feed a healthy population of both SMB and Walleye. If it were me, I would either buy or trap myself some of the minnows and sort them individually before adding to the pond. I am planning a similar pond with YP added as an intermediate species to provide some additional SMB and WE forage. I would still feed if I had SMB and/or YP available that were feed trained, but at least you would have some other natural forage available.