Fathead Minnow vs Bullhead

I'm building a rainwater pond this year. I expect it to be a minimum of 4,500 gallons after the first 12 months and it will be able to grow annually for a while. We get about 27 inches of rain annually, plus around four or so feet of snowmelt. I have a natural pit area, but will dig it out a bit steeper to make roughly a 25-foot wide, 7-foot deep pool in the center. Based on a similar farm pond in the area, I would think that would hold fish through winter. I want to have fish in it both to grow food and to make the water more fertile for garden use. My first thought was bullhead because it's common knowledge around here that they can handle lower oxygen and warmer, shallower water than other gamefish. I have also read about fathead minnows as less of a food crop but more of animal feed. Does anyone have any opinions on the matter? Zone 5, Michigan.

Try a few of both species at the same time. Bullheads grow slowly, especially in zone 5. Fatheads don't grow much over 3" but they're prolific if they have the right spawning conditions. They fill different niches in a pond. Bullheads are mostly bottom feeders. Fatheads are midwater and top feeders. Fatheads make excellent bait for catching game fish that you can eat. You will know if you have a viable system if the fish survive and reproduce next spring.
In any case you won't get much growth or survival in a brand new small pond without some supplemental feeding.

Jordy, I would be concerned about the 7' depth during a cold Winter in your area. You might want to consult a professional pond company. My guess is, they will probably suggest an aerator.
If you are wanting fish for food, Channel catfish are pretty hardy. (and tasty!) My sister lives about 100 miles to your South and has Channel Cats, Bass, Bluegill and a few Crappie. Here is the company that supplies there fish and pond maintenance know-how...Her pond is pristine;
https://joneslakemanagement.com/

Carp, if you'd eat it.  Not the fancy, Koi variety.   Or, as mentioned already, a cat fish.

If you put bass in make sure the other fish are large enough that the bsss can't eat them.  Make sure you don't over stock it.  Are you planning on feeding the fish?

Another thing to consider is whether your addition could become an invasive species. It'd be soooo sooo sad to damage the native populations if something extreme/completely unexpected were to happen and your pond fish got into the local stream, river, or lake.  And/or if your pond fish brought along an invasive plant species in their gut, gills, or in the water you get them in.