Halfway through, I think that a lot of the manifesto is drenched in hindsight, rationalizations and bias. He seems to ascribe a lot of elaborate motivations, make tenuous connections and wonky reasons for why he is the way he is ("I was so bored I had to be weird" is a classic). I have trouble taking much of what he writes about his teens, at least, without a big pinch of salt. Stripping away the melodrama and presumed exaggerations, it sounds like he had a pretty ordinary, if somewhat troubled and frustrated, lonely teen life. His supposed radicalizations later aren't that unusual either.
Narcissistic tendencies seem pretty obviously present, although I'm not really seeing him being divorced from reality yet. Having delusions of grandeur and being self-obsessed, though? Yes.