A couple of thoughts. First, a couple dozen minnows in acre(playing area of a football field) are going to have trouble even finding each other, much less reproducing.
START SLOW and make sure you understand your goals and that they are realistic.

Maybe a retention pond company can dig a hole and stop up one end. But, you are building a home for fish and for family enjoyment. . There is a difference.

Your first investment will be information/knowledge.

Start with Mike Otto's book "Just Add Water". Mike has been pushing dirt for a long time. Study dirt. Some of it holds water and some doesn't. A mixture of clay/dirt or sandy loam works best by an operator who specializes in ponds. There is no shortage of good old boys who can cut grade and clear out trees but, ask if they have ever built a keyway. Ask to see their work. My best advice on dozer guys is to drive around the area looking for ponds. If/when you see one stop and introduce yourself. Ask who built it and what would they have done differently. Who built it and would they use them again.

Don't get in a hurry.

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP