Various answers
Page 155
I agree with your first translation.
In the second one, I believe “起きる” is being used in the sense of “to occur” or “to happen” => “I wonder where was such a big bug was happening…”
どこで here would be どこ (where) + で (particle) - the latter can be used to indicate the location of an event.
Page 160
Yes - Kon feels Kasane’s explanation makes a lot of sense given the things that have happened to him today.
Page 162
Not confident on this one, but my interpretation is the following.
生まれてくる means that someone was born, and the came to a certain point in time which is not necessarily immediately after being born. Take for example the expression:
So here, the person is born first, then after an unspecified time, they experience a certain thing for the first time. Like in that jisho example sentence, they drink a lot for the first time (which obviously didn’t happen when they were still a baby).
I feel Kasane is using 生まれてくる in a double sense here. In Kon’s case, he was born immediately as some people’s roommate, and as some people’s friends (like a person would be born someone’s child or relative). However, Kasane feels this is not very different from a normal person that is born, and after certain time, becomes friend or roommates with others - the “come into someone’s life” is not very different from “being born into their life” from the roommate or friend’s point of view.
I believe the って is the casual quotation marker particle.
I believe だけで here means “just by”. Just by (saying) “People are born 0 years old as someone’s child” (you could also say) “Sometimes there are people that are born 14 years old as someone’s roommate”
Page 168
I feel this is quite ambiguous, but my interpretation is that まともな is more like “proper” or “sensible” here. Since there’s always a bug going on that makes things wacky, it’s kind hard to feel the world is in a correct state.
Page 175
Yes, that’s my interpretation too.