Well water is probably better than city water because of no added chemicals. One could argue that well water could get contaminated by run off chemicals but ehh most likely not.
IMO yes. as long as your water is still within parameters. well water should not have anything in it. the PH is going to be differnt from well to well so you will deffinately check that. Run a full range of tests on it so you know exactly what you are putting in your tank. but like i said, if the water is within parameter, it s good, additives or not. what are you keeping inside?