FWIW: Midwest Dave is correct as to IL regulations for getting fish. I don't remember the size of his pond; but I would compare prices and probably go with the state supplied fish with some purchased from selected breeders to add into the mix.
I have pics of some Rosey Red fathead minnows that arrived mostly dead and with a whole bunch of other fish types (plus a crayfish) included. I bought those from a fish breeder. You can't just assume that you will get better results from a breeder vs. the state so I would most certainly take a look at all the fish (from whatever source they come) before they went into the lake. The supplier made good by sending another shipment; but I purchased from Anderson's the next time and inspected them closely (and was much more impressed).
I would also - to the greatest extent feasible - ensure that fish won't be able to get into your pond either upstream (flow into your pond from a stream or another pond) or downstream (swim up your pond's overflow) from a stream or another pond.