Crafting system needs to take stuff/loot we find on an adventure and turn it into stuff we want.
So at the base level I want loot that has a ready GP value such that if I DONT craft, I can sell the loot for cash equivalent. Even at the point of acquisition. DM can say “you snag X coins and 3 steel ingots (whatever) worth Y coins,” and then I can either write down X+Y coins or track the materials. Of course that means either deliberate treasure placement on monsters or in adventures.
It also implies a wealth-by-level advancement. More likely by tier.
And I want to take that loot, compare it to a crafting list in the book, and “buy” the crafted item by exchanging the loot and the time for the item. That means each item needs a “recipe” of its own. Although those recipes can be formulaic. So I also want a table with those collected recipes so that I can quickly go through.
I want crafting to grant access to items that are not traditionally available through the market, and to equate to something like a 10% to 25% discount from the market price of those things that ARE traditionally available (the time spent as an opportunity cost accounts for the price drop). So I can get platemail at a 20% discount but it’ll take 2 or 3 weeks (or whatever) - do we HAVE 2 or 3 weeks to spare right now? Or I can supply some potent healing potions that I know we’ll need but nobody is selling, and we’ll need to wait a few days to brew them.