Ideas on lake stocking?

Stick with native fishes, especially if the pond is somehow connected to another body of water. Native minnows are fine, along with something that will eat them. As far as the insects, reptiles, and amphibians go, they will arrive naturally if the pond is not disturbed. Definitely, do not release koi. I wouldn't be too keen on the gars either. Decide what you want from the pond (sport? food?) and pick the fish on that basis.