My first question is about the "Headband of Vast Int". If I were to create a "Headband of Vast Int" would I be allowed to have the knowledge skills associated with the increase to Int be ones I don't have any ranks in? I thought I saw somewhere a while ago something that said I have to have at least 1 rank in the chosen skill but after going through everything I can think of I don't see anything stating that.
Next I know that I can make items with MetaMagic feats in them but if I lack the feat can I increase the DC of the spell so that I can add the feat? I know that it says you can except for a lack of the spell but it doesn't specify about metamagic feats so I thought I would check.
There's no such requirement for crafting the headband. So RAW you can attach any skill you want.
FAQ about almost that
I would say no(but I'm not adamant about it). You can't create potions, spell-trigger, or spell-completion items without meeting spell prerequisites. So to make a wand of magic missile with the reach metamagic feat applied, you need the feated version of the spell available(scrolls, metamagic rod, other caster, etc.).
For other items, it's just a +5 DC for not having that spell(metamagicked version).