The hoppers aren't my idea, but they work very well. I think i saw them used on forgecraft once. If you have the same item in multiple pedestals, you only need to fill one of the hoppers. As the item is used, the altar will continue taking the item again from the same pedestal. It was a little disconcerting the first time i saw that, but it works just fine. Extra items are fine during the crafting. As long as the item is present when the altar needs it, everything is good.
Hmmmm...... sounds more and more like an oppunity for autocrafting