I like this plan - I do believe Standing Column Wells (SCW)  have a place in the geo world - easier on the water supply than open loop but also possibly more efficient AND cheaper to install than vertical closed loop. A similar option is two widely spaced wells, one for supply, one for re-injection.

One clarification I see - he probably figured 2 GPM per ton, so you'd need 8-12 GPM. Here's the approximate math: 5 tons ~ 60,000 Btu per hour. A pint / pound of water takes / gives up 1 BTU per degree. If you pull 10 GPM out of the ground at 52 degrees and return it at 40 degrees, available heat is (10 GPM * 60 minutes / hour * 8.3 pounds / gal * 12 deg (52-40)) = 60,000 BTUH.

The above is simplified, ignoring, among other things, heat added by operation of the compressor itself, but it serves to illustrate what goes on on the water side. In summer, situation is reversed but math stays essentially similar - groundwater is supplied at 52 and returned at 64 (again, ignoring compressor work)

2 Caveats:

1) Water temperature conditions tend to be more favorable / efficient in open loop or SCW applications, but pump power may be much higher, especially for open loop. It takes much more power to lift water from down a well and dump it than to merely circulate it around a closed loop.

2) Open loop and SCWs are vulnerable to problems from poor water quality - scaling or sedimentation can impede heat transfer. A good installer would measure and record elctrical current and or refrigeration pressures during commissioning and check those values during annual maintenance - any loss of efficiency owing to scaling or sediment could be remedied by flushing / washing heat exchanger - easy to do with provision of valves for the purpose.

Good luck with this - keep us advised of progress and if any more questions arise - getting the air side right is every bit as important as the water side.

As I understood it (and I may be wrong), the nominal supply required was effectively 0 GPM, since water is being drawn and dumped at the same rate.  The only time the 2GPM comes into play is when the system goes into "bleed" mode, which would happen when the standing column's temperature gets too high and it's necessary to bleed off some of the warm water so that it is replaced with cooler ground water.

But in relation to your BTU math, he also said that there was a minimum size of the water column that came into play, which essentially determines the thermal capacity of the well.  I presume that this in turn interacts with the surface area of the well, which determines the rate of heat exchange with the ground.

Or is this layman missing something big...?

Don't confuse net flow out of the well with the flow needed through the heat pump. While the net for the well might be 0, the heat pumps need at least 2 gpm per ton.

Update: the 8-ton folks called back, and are coming out next week to look at the house.  He was extremely unspecific in his recommendations or rough pricing, saying he really needed to see the house.  So, okay, come on over...

They definitely are working with a handicap, but on the other hand I'm having trouble getting return calls from the first two folks.

The difference in square footage between the sample blueprints and my computations continued to bug me.  So I remeasured the interior (overall dimension), which gives me 2,600 sq ft above plus 450 sq ft below, which is much more in line with my room-by-room data in HVAC Calc.  Turns out the dimensions on the builders samples were larger than the actual house.