HolyJoker
A selfish MC is a smart MC, being thrown in a world were death is just around the corner, a world where kids are sent to war and villiages fight for power, being the way he is, is basically his best weapon. Not like those MCs who give there secrets like champions and go a step further and try to save people they met for 2 seconds.
Im kinda salty about him killing his teammates(indirectly and directly) but not much. I mean at least make him care a little. Also he should learn more medical jutsu and seals. He make regeneration seal by compressing a purifying medical chakra, it could help a lot in both battle and physical training. Just saying.
He is not considering the other possibility, although his reasoning behind his actions is quite possible and reasonable. It could be that from the beginning the MC's soul was always her son. And there was never another soul, out of all the fanfic I've read, I never read one that at least considered the possibility of that happening, even though they (MC) don't know anything about Samsara. Just because they are souls from another world / universe, they assume that there was already a soul in the body.
Totally disagree about how thinks of his mother. She seems like a worrywort that only want to love and be loved. If he told her he remembers his past life she would be confused and never truly understand but tell him that she loves him. Having said that it’s highly likely she will spill his secrets if she gets cornered by Jonin so yeah don’t tell her anything for both of their sakes.