Would like to here from anyone who has done something similar. Things to consider in my planning, potential pitfalls, cost, lessons learned, etc.
I used the house well to help keep my pond up this year. While I couldn't keep it full, I was able to keep it about 12"-18" higher than surrounding ponds in the area.
Planning: Make sure you have enough water flow out of the well to fill the pond taking into consideration how much water leaks out. If I was to drill a well specifically for the pond, I'd rather drill one that will pump out a huge volume of water in a short amount of time and rig it up to an automatic float system so it would turn itself on and off if I wasn't at the pond on a daily basis.
My reasoning is that if I have to pump cool water into the pond continually, I might keep the water temp down, maybe too far for optimum growth for warm water species if I was continually adding cool water (as I would do if I didn't have a lot of flow). Adding a big shot of water might let it warm up before another shot was needed. I'd also look into adding the water to the lowest (i.e. deepest) part of the pond. That way you wouldn't be diluting the warmer top water and you would be adding oxygen to the cooler water on the bottom.
I don't know how cold it gets by you, but here I would need to plan on keeping the line going to the pond unfrozen the whole year, or drain it for the winter.
I know the water here is good to put in the pond. Cecil has high iron, so he needs to remove some of the iron before it goes to the pond. Also, well water has zero or very little oxygen in it. It also could have dissolved gasses in it that would be detremental to the fish. If you were to run the water over a bunch of rocks, splashing it around before it entered the pond it would add O2 and remove the dissolved gasses. Cecil did the same thing by running the water thru a stacked column of buckets filled with hollow plastic spheres.
Pumps wear faster when they are shut off and turned on. For something like you are describing, running it without a bladder tank is best.
For water volume, my wells' output is 28 gpm. That isn't enough to keep up with the leakage from my pond AND fill it more than 1/4" per day. If I were to sink a well for the pond it'd have to be 75 to 100 GPM.
Costs vary too much from region to region. Electric would be easy to figure, just go on the hp rating of the motor. I'd put a double or triple screen at the bottom of the well if possible - less to plug up. The house well has a double screen (it's a 4" well) and the driller said it was capable of pumping 100 gpm with the appropriately sized motor.