From what I understand, some people with whom I am acquainted, who are "in the know" tell me that the cost of a ground source heat pump, if factored in to your mortgage, saves more energy costs, than what the mortgage hit is. In other words, a guy might add 100 bucks monthly to his mortgage, but save 125 in heating cooling costs. Actually you wouldn't be heating the water in the winter, you'd be cooling it, and heating the house with the extracted energy, then the water discharge bleeds into your pond. Just a thought.
To start you need to ascertain from your dirt guy how compactable the soils are, and if you can expect a seal that will allow you to discharge water into the pond faster than what you are losing to evaporation + seepage - rainfall. You're probably OK, but make sure.
Then if you are certain you will maintain a full pond for the most part, the derivation of your water will dictate the numbers and types of fish you can expect to thrive in your pond. Water that can be replaced periodically through rainfall and well discharge will support more fish than a stagnant pond. Well water discharge, if you can provide a particular gpm, may allow you to "play" a little more with cool water species.
This is exciting, and your pond is absolutely big enough to do some really cool things, but I think it would help to go through this step by step.
Bruce
