Are we talking kingsfoil and deer blood, essence from leylines, displacer beast tendrils and owlbear beaks, or the souls of their fallen foes?
Yes. And also metals, woods, leathers, etc. All of the things and then some for good measure.
Think Runescape but without the obnoxious grind and repetition.
Next, what are you thinking the average success ratio should be?
That depends on the crafting system in question. To keep it short, I call my own system 7 Dice. You roll 7 standard RPG dice and from these you can derive 6 different values that correspond to different aspects of the crafting process, which each confer different properties and can integrare different crafting components.
Each value can be lowered or increased utilizing a "crafting budget" (a combo of skill modifiers, energy mods, and appropriate class features) and once you've set each one, you total everything and this determines the DC to confirm the item, against which your skill roll is compared.
Most "novice" and "apprentice" level items will be very unlikely to fail, but the chances to confirm better ones increases exponentially, and in turn are more costly to your crafting budgets in the first place; you won't be making mastercraft items without being effectively a master, or getting extremely lucky.
This is also helped along as any excess crafting budget you have (such as from skipping a special component, or even skipping a standard one; you don't necessarily
need a scabbard or a hilt after all). So in the mid levels you'll be able to train pretty consistently without having to waste materials, and by later levels you'll be able to scavenge useable items even if you're not able to confirm the crafted item you intended.
In this case if we're talking potions, may be you lose out on a spiffy 6d12 Mana potion, but you might get a 1d12 one instead. (I made those numbers up)
Will finding needed resources (and being able to craft/refine them) be an easy or a difficult process?
Depends on the resource, and I wouldn't include refining myself; Id assume that as part of the crafting process if it isn't explicitly already in there. (In my system, smelting and tanning is assumed as part of crafting martial weapons and armor, as is spinning and carving for their magical counterparts).
How much time would the process take? (Weeks, days, hours?)
Im personally partial to skipping the time gating as a matter of fun (particularly to avoid tedium; part of what I wanted my crafting system to enable was something you could quickly run at the table but it still felt like you were actually doing something), but most things we can get some reasonable timeframes, and they could have induced time modifiers introduced at higher crafting budgets.
In a high fantasy world most weapons and armor aren't going to take long to make, and will be well within your typical downtimes for an adventuring party. Potions and the like, especially basic ones, could even be done in-situ, though more complex and powerful brews should require substantive brewing time.
What time gating can enable is more depth, as this is good fodder for tools and equipment to also have tiers that help offset the chances of failure, especially for stuff that the character has to just let sit somewhere. Tools and equipment in fact can even be craftable objects unto themselves, something you make so you can chain them into better items, which enable you to go into more dangerous areas, which get you better components to make better tools to make better items and so on.
Thats a whole ass gameplay loop right there.
Indeed. Runescape is one of the formative experiences Ive had with RPGs of any kind and has remained a consistent influence on my preferences and thinking for how RPGs ought to be structured. Its skill system and how its integrated into adventuring in particular is a big time inspiration more games, especially TTRPGs, should learn from.
