Our population as of Valentine's Day. Notice the little orange babies? There are five more black ones that will eventually turn white, orange or a combination.
Boy have I got a deal for you. You could buy a few little ones from a local pet store and watch them grow, but what about having some BIG ones to kick your pond off right? Probably won't hurt to get a few "new" ones anyway, but.....
Each year we try to give away goldfish to keep our population down and improve the health of all. We need to lighten the population by about 20 fish so let us know and we can give you some. Have your pond already established but the cold/cool weather is a good time to transfer to avoid too much shock.
We've given to neighbors until they turn away when they see us with buckets. One of our friends puts them in some springs and apparently they adapt quite well to not being fed every day. They must feed on Natures bounty and keep his springs clear of algae growth.
We feed them every day during the summer, cut back on cold days, go to every other day for extended cold periods or even stop for days on end in extremely cold weather or when it freezes over. Tough to get that food through the ice.
I would suggest you feed as well, especially if the pond is too small to support its own ecosystem but it does not need to be excessive and in fact shouldn't or you will end up like us with fat, over productive fish. Overfeeding also causes issues with the uneaten food as it decomposes. I think a guideline is to feed what they will finish in about 5 minutes.
They do tend to eat frog eggs so if you want a pond full of frogs, this may not be for you, but we manage to have a small population anyway. We even hosted a snapping turtle for a few years. We never found any missing or injured goldfish (we fed Snappy too) and after two years he went on his own walk-about.
Plan on circulating water or putting an aeration pump in. Without that they will suffocate from lack of oxygen, especially a it gets hot. We keep an extra pump handy to fill in when our "stream" pump dies. A day or two loss during the summer for a small pond could kill many of your fish.
If your pond is shallow and away from the house, watch for egrets. Those leggy birds you might see standing in shallow streams. They are great fishers. Ours is close and has cats and dogs always close. In fact, our dogs take baths in there, even in the winter.