Don't put the cart before the horse. When knocking a well in like your doing, your driving the pipe blindly. So check often with the Pitcher Pump. Most people drive points in 5 foot sections so they can do just that. The only way your going to know what material your in is to drill the well the way a driller would by putting in a joint of pipe then drilling ahead and looking at the material coming up. Your looking for clean sand and/or gravel. Not dirty stuff. Once you get this well done, and have done a pump test with a rented pump or just the Pitcher pump, you can then size a pump to fit the well. Then the sprinklers will have to be installed to fit the system.
bob...