Feeder guppies have two type.. the colourful type and the greyish unattractive types. The colourful types were kept in better conditions because they are mostly culls from fish farms (beautiful ones exported or sold locally, those that don't make the grade are removed as 'culls'). Those that are greyish were never bred for other intentions other than as feeders.
While guppy is not a high waste fish, due to their size a lot of them are squeezed into a bag. If you keep so many feeder fish, even if each produce a little waste it will still add up to a lot! If you plan to space out feeding them to your fish instead of all in one shot, you should change water frequently in the feeder tank and feed minimally. Due to the overcrowding you should provide aeration. You should also add some salt to the feeder tank to keep possible parasites. The increased salinity will also make them happy because they are brackish water fish. You don't need to measure it exactly, for a two feet tank, a handful of salt is just right. If you use a larger or smaller feeder tank, just adjust your estimation accordingly. Note: Subsequent dosing of salt after water change should be in lesser amount, depending on how much water change you do.