You have done a nice job and don't second guess yourself, because its too late anyway. I have installed somewhere around 40 water features and all but two of those had a pond os the major feature. One was a disappearing stream that flowed from under a boulder and ran about 30 feet down hill and disappeared . One was pumping for a river up a small cliff to create a 30 foot waterfall. All the others were ponds with falls or fountains. The major one I have in my yard was the first one I did, about 30 years ago. Still works fine but every time I installed a pond I came up with "what if?" I'm too old now to think about doing it again. Besides, there is a 30-35 foot bald cypress in it.
You don't need to winter your fish in an aquarium. I am in zone 6 and a stones throw from zone 5 and my fish have never succumbed to the cold even at -14 degrees. My butterfly koi in the larger pond have spawned babies which are now pretty large. The fantails in the smaller pond also make it through winter unscathed. I have lost fish to Heron, racoon, bear, water snake and bullfrog. There are several things to help limit this, but its going to happen.