Just because you have 50 feet of water in the well, doesn’t mean it will make enough to run a sprinkler. Of course you won’t know until you try. Use a ˝ HP, 10 or 7 GPM pump, set at 120’. A ball valve on the discharge pipe will let you vary the flow out of the system. Try running wide open and see if it holds up. If not shut the ball valve back to 5 GPM and see how long it will run. You have to find out if water will come into the well fast enough to do what you want. The well may only make 1 or 2 GPM for long term. Or it may not make any. You just have to run it to see.