Mrs Spud, you have a wonderful setup, the potential for a handpump during power outages will keep you in the wet,
, and it sounds like freezing won't be an issue either, or protecting it from that anyway. All your plumbing can be done with CPVC or copper, each is pretty easy, I favor copper always for supply plumbing, and just a few components will set you up, I'd recommend schedule 100 pvc for the long run down to the water-typical for wells- then, may I suggest a variable speed pump, it will adjust pressure based on demand, cost is not too bad, but it's like having constant city pressure regardless of how many taps are open. Electrical use is more efficient because of this and no need for a pressure tank(yay), so take the time to figure this out, you could run a small ad for a plumber to do a side job, or call some in the area and find out if they'll come and do a side job. The backflow valve is real common, they are necessary for sump pump disharge lines, again check the hardware/home improvment store.
Keep us posted on this, sounds like a fun project, you could cut your water bill for washing clothes with a bypass valve
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Since you realized water at 34 of a 340 ft well, may I recommend a draw-down test, get a pump-a sumppump will do, cheap to rent- run a 100'x3/4" hose into the well and to the intake of the pump, then a short hose, 10'x3/4" to the outfeed of the pump, you are looking for 7-9 gallons per minute for at LEAST 5minutes without sputtering. A simple measurement method is; have a measured 5-gal bucket and a watch with a second hand, when the bucket is full, time it, how much time to get 5gals, this works better if you can have 2-3 buckets lined up, two thirty gallon trash cans with a plastic bag as a sealed liner would work fine too, then you time 60gal in 5minutes equals 12 gal/min, which would be great, but 7-9gal/min will suffice. Pump size, a 1/4 hp will work, but a 1/2hp will be better and won't work as hard. If you perform this test and get sputtering, then you know to add another 100' hose and repeat the test, now, the rented pump may not be able to draw that water up that far or it may collapse the hose, testing the cheap and dirty way has it's frustrations. Something else you can do is find out who the previous owners were and ask them what the output of the well was when it was in use. OR Call and ask a well company if a test can be done on a well of your description, a phone call will keep you anonymous.
My fingers are starting to cramp, let us know where this goes, I am hitting tilt on my knowledge base regarding this though.