So it turns out that the spots I had in mind for the water storage tank aren't quite as high up as I thought. The first is only 20' up from the farmhouse and the second is only 30' up, nowhere near the 100' I was hoping for. Having the tank up 100' would provide enough gravity-fed pressure for basically anything we want to do. There are higher elevation parts of our land but they present at least a moderate access challenge due to the forest overgrowth. On our next trip we'll do a bit of bushwhacking to see if we can find a suitable site.