The questions apply to a character with the required crafting feats, along with Idealize as a discovery, and Transmuter as a trait.
http://www.d20pfsrd.com/classes/core-classes/wizard/arcane-discoveries/arca ne-discoveries-paizo/idealize-su
http://www.d20pfsrd.com/traits/magic-traits/transmuter-magic
1. If I craft an item like a Headband of Alluring Charisma, does it benefit from Idealize or Transmuter?
2. Do Idealize and Transmuter stack, at all?
1. No - The ability score increase from a headband is not a transmutation spell
2. If the spell is a transmutation spell that grants an enhancement bonus to an ability score, it would benefit from both (+1 CL and +2 to any enhancement bonuses to ability scores).