You must have a really large pond for all those fish. How big of a heater would that take? Mine is pretty small. The first yr. I brought the fish in the basement put in a kids pool (with a drain hole in the bottom to get rid of the water in the
spring).They were shubumkin or fantail don't remember. They did ok. The basement is not heated but wont freeze. The fish didn't eat or barely move all winter. That was the yr. they mated early. The next yr. I left them in the pond. The water froze but not clear through. The fish did ok then too. They didn't mate that yr.
So I'd guess that you could do either one. Just remember if you leave them in and don't have a heater don't break the ice open that forms on top. I have read that dead leaves and
plants left in the bottom can do bad things to the water. But I noticed that the frogs and fish hide in the leaves on the bottom.
I would not worry about the snails and algea eaters they probably wont make it through the winter. Course I'm just a beginner too. And things work /or don't work when you least expect them to.