So INT4, WIS12, and CHA19? This is a perfectly functional person (since he has so many friends to help him out!). Can't learn new things very well or quickly and always gets the long words wrong. Probably can't spell worth a lick and doesn't bother with math more difficult than you'd see on Dora the Explorer. So, notably stupid. This isn't the guy you want as a manager, but quite likely as a motivational speaker.
As for the complexity of the plan, I would only be a tiny bit surprised if my three-year-old daughter came up with the same plan. Just think, this is a sorcerer- he just "gets" invisibility. Magic is how to overcome obstacles to INT4 sorcerer. That high charisma could probably be used to convince the gaoler to release his friends, but it's not what he did. He did magic! He actually did something stupid, given the resources available- he made his friends fugitives.
"But he hid the key!" Yup. With an understanding of the limits of his spell, which he does have, and a positive modifier for wisdom, why does this seem unreasonable?