I'm no literary expert, not even someone who reads on a regular basis, and I think you did fine introducing spellcasters.
It makes sense to me why Jamie would choose that path. He's already lost his sister. He feels powerless. The way I see it, he feels like this is one chance to take control of a situation that might otherwise be out of his control. Becoming a doctor would take too long.
As for the selfie part, it made me lol. It does seem like a "typical teen" thing to do. It also helps to remind the reader that he is in fact a teen. When you remember that fact, you realize even more the struggles he's been through in his short life.
