2] 10-3 runs is a lot of electricity. And wire. Seems excessive
1" should be large enough
You can use a small submersible in the house 1000g tank with a Franklin pumptek to keep it from pumping dry.
Then a float switch in the 1000g tank to turn the spring pump on. Choke back the outlet of the spring pump into the 1000g tank with a valve until it matches the spring water input to the cistern.
What is the production in GPM of the spring?