Eric - 500 perch and 500 SMB in a 0.25 acre pond is very unrealistic especially without artificial feeding. Based on this, I would always get a second opinion from whatever this fish hatchery guy tells you. 100 perch is about correct for a 0.25 acre with out feeding. If you stock even fewer perch (75-80) they will grow faster but more importantly the minnows will last longer.
100 perch growing in your region one year from now with ample food should have lengths that range between 5" to 8" (July05). To get to this size they should consume about 100 lbs of minnows plus invertebrates during the next year. This is why Brian says they tend to wipe fatheads out fast without lots of cover. Fatheads are slow swimmers and quite vulnerable to perch predation.
Extrapolating;; with fatheads at 1.5", there are about 740 per pound. 100 lbs of fatheads equals about 70,000 fatheads. Hopefully your pond has enough to maintain growth of 100 perch. That is only 700 fatheads per each perch's consumption for one whole year. They could eat 2 or 3 small minnows per day when feeding good and water is above 50F. Perch also feed often in late fall, under ice in winter and in early spring for egg development which starts in August. This food base estimate may be on the low side. I know it is on the low side for larger perch than those you will have the first year.
Keep us posted on your progress. Come to this same "Two Fold Question When to.." topic post, and add to it, every now and then so we can learn more about the growth of perch, fatheads, and SMB in small NY ponds. I am especially interested in how the fatheads are doing and about the current perch growth & sizes. Sample them occassionally with hook and line. Perch will readily bite a small hook (No.6 or 8) with piece of worm once they are 3" long. If 2" perch are stocked now in your pond they should easily be 3" long by middle of August; and 5" to 6" buy end of October. Report back on growth, let's see how far I miss the estimates.
FYI. This year's perch hatch in my pond are 2.5"-3.5" long (July 10). I am about same latitude and growing regiion as you. The hatchery perch are crowded and not getfing enough to eat, thus they are smaller. This is fairly typical for fish at many hatheries.
