Repeatable Quest #4 requires Pure Copper Ore, 4 per turn-in (2 for each of 2 items). No-one will have enough to work their way through the several levels before skill level #12, where the quest changes to #5, which does not need special materials. To accomplish this, you will need to gather incrediable amounts of pynwood/copper ore (thousands of units, all told) to make items near the top of your ability that give the best skill XP per resource.
At the last stage, the best item to build is the Refined Copper Wrist Blade, which requires 12 copper bars (plus bought items) to make. This gives the best XP, as far as I can tell, at ~218 XP per unit.
But here is the warning. Keep as many of these you make as possible for your bags to hold!!!
Vendor only those you must for space reasons. Because this is precisely one of the 2 items needed for Weaponsmithing quest #5! The other item is the Improved Copper Throwing Blade, which gives a little less at ~195 XP per unit, and requires 16 copper bars to make. But the #5 quest turn-in is worth ~849 XP.
I was lucky enough to check the new quest the trainer was offering before vendoring the last batch of wrist blades, and I ended up having 13 of them already made to get a big jump on completing the next skill level. But I wish now that I had saved more (having vendored all the prior batches).
Just a word to the wise.