Every 2 points of Intelligence reduces cooldowns by 1. So instead of being any sort of "hard" thing, it's best to look at what spells you're using and determine how much you need to reduce the cooldowns. For example, 16 Int allows you to cast 1 Feather Drop every turn.
Alternatively, each point is 5% additional status effect chance, so you can figure out how much Int you need to get a 100% status chance. For example, 18 Int gives Lightning Bolt a 100% chance to Stun.
You really need to consult your intended spelllist to know which values are best for you.
