Have you calculated your heat requirement maximum and average?
I do not mean the standard sizing.
How much energy do you need a day? Then how many run hours
Do you have a log burner.
What will be the SST of your geothermal heat pump.
What is the average air temp over the heating season( you will be surprised), knowing this what will be you average SST with a air source heat pump.
Are you looking at doing your DHW with this heat pump (I would)
Also what are your 9or the wife) exceptions from this system. (clue they very slow in reacting to changes in temp)