although i dont like it, i know feederfish are needed, buy from the lfs, there cheap, and you can at least give them a decent life for awhile.
tanking fish from a pond is wrong though, just becase there are alot, doesnt mean its ok. i dunno how many you'd like to take, but by taking fish from a pond/stream your denying crawfish and larger fish a possible meal in the future. also i feel its wrong to take an animal from its natural habitat and tossing it in a tank where it has no chance to escape a predator, your denying it the chance to prosper, and to be free, which it was born into.
also, i dont know how your going to manage treated all the diseases at once, since i beleive some meds compromise other ones, you'd have to treat for ich, fin & tail rot, mouth rot, internal fugi... not to mention local bacteria and diseases that may not have any symptoms.
plus theres always parisites, if they can live inside the stomach of a wild fish, they can live inside the stomach of anything that eats it's host, and they are much more common in the wild, as opposed to captive bred.