That's a good question. We'll probably move again by then, so the space will determine the size a bit. I always sort of use 1000 gallons as a reference point because it is a nice big, round number and I have seen that as a recommended minimum for a koi pond.
A lot of the planning has to do with this idea i have to make a miniature fishing village on the edge of the pond. I am a sculptor with some experience with miniatures. Wakins grow to 18 inches. There is something completely hysterical to me about the idea of all these fishing boats tied up and the fish below the surface are larger than they are. Like something from a dream.