First off, I'm not an engineer. Your idea seems to have some merits and if you want to try it, that's awesome. I don't want to kill your wort chiller dreams.
I would think a standard 50 ft. wort chiller would do the job and keep things simple. The chilling of wort is a function of the amount of tubing in the wort, plus your ground water temperature and flow rate. It seems like your design might increase the total amount of copper for chilling, but the benefits of that might be neglible given your water's temperature and flow rate. It's difficult to determine without knowing the other variables, but that's my understanding of the physics involved in wort chilling. I hope this helps.