I never have anymore space

[PArcher]

SNIP

Honestly, a serious crafter should know most of that already, or know where to find that info very quickly.

Or, at the very least, have a list of things they make a lot and their mats, and keep those things (or the pre-mats) in stock.

Rare (AKA expensive) ingredients should also be kept if you plan on using them, or sell them if not.

Also, I would keep NQ stuff, sell HQ stuff (except for 1* mats [Twinthread, Rose Gold Nuggets, etc]) since if you're able to HQ 2*s, you can HQ 1*s and lower with all NQ mats without issues.

[Niwashi]

Honestly, a serious crafter should know most of that already,

Not really, as the answers are constantly changing. What you need at one point in the game isn't what you need at another point in the game. After a productive gaming session, you're likely to have advanced at least one class or another in either level or gear, so what that class needs will be different than it was the day before.

or know where to find that info very quickly.

There is no place to find it quickly. There are places to look up each step of the process, but then you still have to put all the pieces together yourself, and that's the time-consuming part I was talking about. So you can look up ingredient A to find it's used in making ingredients B, C, and D as well as final items X, Y and Z, but then you need to look up what ingredients B, C, and D are used for, etc., until you finally put together a long list of final items that ingredient A goes into. At that point, you need to start considering whether you'll want any of those final items, so need to go to a different site to look up leves and GC supply missions, as well as checking in-game for which items you have or want for yourself. That's a lot of work just for determining "should I keep ingredient A or not?"

(Actually, there's a pretty good site for going the other way around. When you want to make something, you can in a single step find all the root elements as well as intermediates you'll need to make it. It doesn't, however, go the other way around, and tell you what all items a given ingredient is needed for. And even if it did, there would still be a separate step to check whether you'll want any of those items.)

[PArcher]

SNIP

Really, there's only one crafter that has confusing, unnecessarily wasteful recipes: CUL.

All others generally use the same materials for each "tier" of gear (and ARM/BSM share them, making it even simpler)

I keep Iron Ore, Bomb Ash, Brass Ingots, Silver Ingots, Mythril Ingots, Electrum Ingots, Colbalt Ore, each type of thread (except Hempen), each type of Lumber, each type of Leather (except Leather and Hard Leather), HQ Undyed Felt, HQ Twinthread, HQ Rose Gold Nuggets, HQ Darksteel Nuggets, HQ Spruce Lumber, HQ Hyppogriff Leather, HQ Shark Oil, Thavnarian Misteltoe and a few (yes few) other ingredients I use and can't remember right now. That's also not counting the stuff I use for my food, since I generally don't keep those mats around, making the food when I get that stuff.

That list makes the vast majority of things, and can be made into other mats. The extra stuff you need isn't needed much, and can be gathered quickly or bought cheaply.