Using a feeder really will save you quite a bit of feed. I use an old hub cap, it has just a small lip, and I set it up on cement blocks, they tend to stand on the ground to eat out of it, although some jump up, but they don't bill it out.
As for the amount, the amount should change with the weather and the seasons. If you free range, it will decrease during the summer bug and green plant season. But with the extreme cold of winter, they need more feed.
I take mine feed everyday, I want it about empty towards the end of the day, if a lot is left, I do not bring quite as much the next day, if it is bone empty, I bring a little more. I think it stays fresher when I bring it out each day. But the gravity feed ones are very nice if you are going to be gone for a couple of days.
Mrs K