Hi there. I'd agree with the previous post that the Chinese have a lot figured out with regard to thermal mass. However, I think
Penn & Cord are better. Even better would be to replace the water in the barrels with 50 psi pressurized ammonia. You'd have to address the safety concern but it would store a
ton of heat.
I've also heard that there are few, if any, profitable aquaponics farms. If they exist, they do it by selling very high-priced basil and lettuce to a high-price market like Chicago.
You also asked about the cold. That's sort-of my specialty. Feel free to get in touch via my blog or check out the
forum about cold weather aquponics on the Aquaponic Source. We have some really experienced folk there that can help.
Some ideas that work well are a passive solar greenhouse like discussed above, plastic or bubble-wrap low tunnels over your beds, air sealing and insulating everything, and freezers for fish tanks.