Quivers?

How many arrows can each quiver hold?
and if the amount is set, how do I go about doing that?

Also, I can't select my arrows on the inventory in game, yet the selector on the Subscreen editor I can...

You need a Bow before you can use Arrows in-game.

Secondly, you change the Quivers' "Increase Amount" in the Item Editor.

Thanks!