Water refresh

Question:

I recently bought a home in Vienna, VA in the Washington DC area. It has a concrete pond that’s about 300 gallons. It has about a dozen goldfish ranging in size from the length of an index finger to tiny — 12 or 13 total. I followed the directions left by the previous owner and yesterday capture the fish and put them in a large container with the original pond water. I then totally emptied the pond, cleaned it out of all debris, and have refilled it with water from the outside faucet. It is chlorinated. I put in the proper amount of chlorine and heavy metal remover (Amquel). Now, looking at various web sites it seems that I should not have removed all the debris or all the water. My questions are (1) is it safe to put the fish back in the pond given that there’s no debris and the pond if full of tap water (albeit treated). (2) There’s a pump in the bottom of the pond that circulates water back to the pond via a waterfall. Does that come out or should I leave it in. Also, what do I do to keep the pipe from freezing if it has water in it? (3) What else do I need to put in the pond (chemicals, etc) to help the fish survive the winter in the DC area? Amd (4) What should I be doing to keep the fish alive in the container while I figure this out? Thanks. Any help is appreciated