If the airator keeps the surface moving all over, you should be ok. As for “ small goldfish “ they don’t stay small. Minnows such as rosy reds do. If you look online, you’ll see that the fancy type goldfish get to be roughly baseball sized, and can’t escape from things like raccoons that may come by, but the common type get to be about a foot long. True minnows will be much smaller and as such, do better in a small pond.
If you go with dunks, research what they contain, as you can expect frogs, toads, and maybe other amphibious creatures which are sensitive even as adults to toxins in the water.