Magic Item Creation [...]
All items have prerequisites in their descriptions. These prerequisites must be met for the item to be created. Most of the time, they take the form of spells that must be known by the item's creator (although access through another magic item or spellcaster is allowed). The DC to create a magic item increases by +5 for each prerequisite the caster does not meet. The only exception to this is the requisite item creation feat, which is mandatory. In addition, you cannot create spell-trigger and spell-completion magic items without meeting their spell prerequisites.
Does brewing a potion only have four prereqs? The Brew Potion feat, knowledge/preparing of the spell, sufficient caster level, and material components (if any)?
I am currently trying to figure out what the finishing DC would be for a level 3 Cleric trying to make a Potion of Haste (not on his spell list). It is my understading that potions can be made without the knowledge of the spell. However, would there also be the prereq of being an Arcane Spellcaster and/or a Wizard or am I thinking too broadly?
Trick with potions is they are not spell trigger nor spell completion items, so the spell is not a mandetory pre-requisite, it's an optoinal pre-requisite (which just increases the DC by 5 if you lack it). So, you CAN make the potion even if you don't have the spell.
The math should be:
Feat - mandetory
Components - mandetory - increases cost
Spell - optional +5DC if without
Level - optional +5DC is short
Base DC - 5+CL (lowest level for Haste is 5th)
So 3rd level cleric making a potion of Haste is 5+5+5+5= DC20
Cost: 375 + a licorice root
If your DM lets you take 10 on Craft & Spellcraft checks (I do), then if you have +10 in spellcraft or craft(alchemy) there's no chance of fail. Takes 2 hours, but can only make 1 a day.