When we built our house, we had a water to air heat pump system installed. It's an "open loop" system, meaning the water that goes though, has to have somewhere to exit. I dug 3 small ponds in stairstep, so the water ran from one to the other. Stocked golden shiners and rosy red fatheads. The shiners reproduce quite well, but for some reason I have to replenish the fatheads once or twice a year. I haven't bought any shiners in three years. Catch them in minnow traps baited with fish food, or cat food.
Try PondBoss forums. They have all the info for you. You just register, like here. Similar format. Lots of info.
The first thing I'd do before stocking minnows, is to kill off any other fish. I know that sounds harsh, but if your goal is to have minnows, they don't need competition.
Btw, you should be able to tell a crappie at a very very young age. Couple of months, 1" should be plenty. Let me expound on that. "Baby" minnows look just like adults, only really really small. The first ones I saw in my pond, I thought they were mosquito larvae until I netted some with an aquarium net. Crappie fry should be no different for ID.
Do gooder since April 26, 2009!