A glass jar should be fine, as long as you leave enough at the bottom to start the next batch off. How much is enough? I would say that 'enough' is an amount that lets you take out a day's fermented food, replace it with water and dry feed, and have the whole jar be just as fermented the next day.
Take how much dry food you get through in a day, then add three times that amount to the jar(s) and add water. When you take anything out, top it back up. It'll take a little while to get going from scratch, and it's much easier to slow down a ferment than to speed it up. I don't know how much acid your well water would need -- take a known quantity of it and add a known quantity of acid and keep testing, then use that dilution. Vinegar is pretty mild, so you can be free with it.
Alternatively, instead of using three days' food, you can use a very small amount and tend it like a sourdough starter while you figure out how the fermenting feed reacts to its environment.