With common carp and bullheads, I am guessing this quarry gets flooded out on occasion. Personally, I don't think I would spend much money on stocking fish that may swim away after a good rain.
That said, fathead minnows are used to supply early growth forage when planning to stock fingerling bass and would do no good for you in this pond now. If I were going to stock fish, I would want to know just what species and size predators are already there. If you happen to have several pound + largemouth, most 6-8" CC will be snacks shortly after being released....so will most BG or RES under 6". Some small stockers may live, but you'll never reliably estimate how many might survive a stocking.
If planning to keep control of the pond for years to come, I'd strongly consider lowering the water level a lot, and killing off all fish with Hydrated Lime and restocking with fish you can control...again, if the pond does not get flooded out regularly.
