Ok your armchair calculations are way off. A 1 inch pipe has a circumference of pi inches, plus a little bit for pipe thickness. Half inch pipe has about half the circumference. Iron is not that much better at conducting heat than poly tubing. The limiting factor is the Earth. More holes spaced far enough apart equals more capacity, don't short circuit yourself trying to get more cold into the Earth (don't make a big underground popsicle). The first two feet might not transfer much heat, the rest will. Try one first, then decide if you are willing to do more. The process sounds difficult, but actually performing the process depends on details. It can be impossible without the proper mindset and equipment.
Read the many examples of what you are trying to do both in AC Hacker's manifesto thread and the individual sagas of others on this forum. With a pump and dump system, you will have all the capacity you need, if your source well will produce enough water and you go big enough on the well pump. A coaxial heat exchanger is highly recommended over a plate exchanger for that configuration. Both a borehole loop and a pump and dump system need a water pump, but the pump and dump system will require a lot more powerful pump to overcome the well head.
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