Every school of magic will have at least a small portion of most things magic can be used for. Damage, healing, utility, support, etc. But some magic will be more specialized in certain fields than others, or feature a balance in certain fields. So something like Fire which is famous for large and powerful blasts of damage can also be used to super-heat a metal cage for escape, or create a soothing campfire to rest at for yourself and allies, among other uses of course. Since every school is similar in that it can be used for many things, I can't really suggest a school for your character to specialize in.
Based on your character's personality and bio, it seems like INT would be an important parameter for him.