From what I've observed, it is far better to store wood moulding flat (horizontal), unless you have a REAL fast turnover! I've seen bins at vendors that store wood moulding vertically and by normal physics, it bows - thus warped moulding.
Our moulding is stored on shelves that my husband built.....they are like compartments. The first 'layer' has about a dozen shelves, 6" deep and various heights. At the end of the shelf is about a 2" lip which he applied sheets of plywood and then built more compartments that are 3" wide. You can keep that up for as many bins that you'd like. On the outside of this, he has one deeper shelf that is for 'incoming' orders - that is where I put the moulding for him to cut. I'd say this unit is 10 feet wide and maybe 10 feet high. This way, we can store the moulding flat; we try to be certain that we place it carefully so one long leg of moulding doesn't rest over another, causing it to warp over time.
We did paint these units and we keep our moulding in sleeves for protection (90% of it).
Regarding metal; we don't store it, we don't cut it - for as little we sell of it, it's not worth the mess.....we get it in chops.
Your question is a good one - I'll be eager to read other's input.