FictionOnlyReader
It's always strange when the so-called 'Reincarnators' obsess with how they have "taken the life" of the one they possess. If your MC feels so bad about it, he can always kill himself. That might return the boy back, or not. Who knows. The morbid humor aside, I feel such ponderings are meaningless drama whose only purpose is to paint the MC as a 'Holier-than-thou' character. It's hypocritical, considering he will not tell the relatives anything about it.
I don't really understand his stereotypical obsession with hiding. I mean sure, if he can't convince anyone to teach him he could somehow get that knowledge, but why bother with all this jazz when asking is easier? :D He could even say something like he wants to know so something like accidental magic doesn't happen anymore, and ofc just so that he can do freaking magic. I mean it's pretty weird he's just sneaking around and quietly getting worked up over this, lol :D I mean it's like he's trying to withdraw his money from the bank, instead of going to clerk and doing withdrawal, he devices elaborate plan to break in and get his money that way.
Honestly, he could just ask for material on wandless magic. I just hope you don't go overboard on that. Proper wandless magic is supposed to be extremely difficult, tiring and can be unreliable/less precise. People use wands for reason. Sure, in few schools it optional, but it's like bow vs gun situation. I think wandless magic should be exclusively just in case method and something he learns very slowly. Before school learning maybe one or two first year spells like levitation spell. Quote from wiki on magic "A wand focuses magic to such a significant degree, that the vast majority of witches and wizards are often powerless without one. However, one can do magic without a wand, though it is often unfocused and uncontrolled. Still, few wizards can perform directed magic without a wand, if they have enough skill and power, but it is still more difficult and tiring. A wizard or witch is at their best when using their own wand: when using another's, one's spells are not as strong as they normally would be, as dictated by the laws of wandlore."
He didn't ask anything about magic for a year? That's bs and the fact that he has the mind of an adult makes it even more stupid. A child is extremely curious about the things that is happening around him/her, it would be a natural thing for a child to ask what is happening. It is weird for him to not ask anything about magic especially when it is happening all around him. He didn't ask his butler, his grandfather or his doting sister. Especially his doting sister that would basically answer everything he would ask. He didn't ask when she came home a few times in the few months after his first accidental magic.