You may have missed my point. You said you do have potentially large fish now, as juveniles (thus small) but my point is that they are potentially large fish, and you should have the necessary facility for them before acquiring them. They will not develop properly in small quarters. And what will you do if the pond never happens?
A basic rule that all of us should follow is never acquire a fish that will become a size that will require a tank larger than what we have when we acquire the fish. In other words, if you do not today have a pond operating, then do not acquire fish that will some day need a pond.