Your tank is large enough for the gar, you just have to keep an eye on the smaller fish when the gar gets larger. If you get the gar @ 6 inches you should have no problem with it getting spooked by other fish because it will have grown up around a variety of fish. The gar will be more than happy in a pond, however I don't know about a florida gar in a pond outside in minnesota though. I would stick to the tank and think about re-locating the smaller fish if needed. You will have a while before it becomes a problem because the gar won't kill somthing it can't swallow, *most of the time*. Sometimes they might try a fish to big for them to eat, but not often.