it sound like this well supplies both the geothermal system and your home. The pump that i reccomend would be a 7 gallon per minute 1 horse power pump. It will start off giving you a good 15 gallons per minute at 40 psi but wont take out any more than what the well produces because the gpm will eventualy level out to the production of the well as the water level drops. That would be the correct pump for that well and what it produces for water. My question for you is how long does the heating sytem call for that 8.6GPM??
As far as the flow for the geothermal unit,i'm not too sure what type of valve you could put in to regulate the water to that 4 psi. Maybe valveman could help you out there.