i'm trying to wrap my head around what you're doing, but a few things..
i'm in northeast ohio near cleveland so can relate to your weather
i'd bury the fish tank at least partially and insulate it.. for that kind of tank, i would only cut an opening in the top big enough to catch the fish out of and reach in with cleaning equipment..
tilapia will grow best with water temps in the 80's, you might get one good season, over winter you need to keep the temps over 60 to keep the fish alive (they won't grow much at cold temps) have you considered "cool water" fish? like yellow perch, trout, or crappie? check with "pond stockers" in your area, or fish farms to see what is available and look up info on the species that interests you..(temps/food conversion ratios, basically any info you can find)..
there's a thread on someone here doing prawns, as well as red claw crayfish, but again, those species prefer pretty warm water from what i've read..good luck and keep us up to date!