You are right that くるくて means (it’s) dark and … It’s the い Adjective て connecting form.
…Tofugu on いAdj and く
Here where I pulled the 見る→ without looking 見ずに from… This grammar point where ず substitute for ない as the negative form
BunPro Verb-ず
The まえ I think it’s a mumbled, flustered version of him calling the 人かげ “おまえ”, but he left off the honorific お…
…お前 (おまえ you; used to be honorific, now quite casual N3 Anime Top 100 )
So then that section “くるくてまえみずに” could mean (It’s) dark and (I) didn’t see you…
(Which is BS, because he was scared, and charged into them on purpose, like a battering ram, but kept looking at the ground, so he could say “Oopsy!” for a purposeful act)
Re. Page 132, sentence 1:
Interesting to me, an Internet search of “Japanese grammar おう sentence end”
brought up this 2018 Wanikani forum thread (!!) which seems directly pertinent! I guess it’s kind of an ancient ghost sentence ending particle?
All that casual speech with the じゃ’s I’m not certain about …
I know for sure that “Nounじゃない” means “it isn’t Noun”… So then that seems to support your instinct that “Nounじゃ” is like “Nounだ”…
I do know that な as a sentence-ending particle is wondering, thinking, musing, and that the あ is item drawn out to show longer thought/musing… So I think that’s what なあ is doing in p.133 sentence 3…
Example: JLPT Sensei on なあ
This Renshuu discussion of じゃ and じゃあ was interesting {especially the part about とにかく(anyway) being derived from an old adage 兎に角 (rabbitにhorns)!} … But it didn’t seem to address what we’re struggling with
I just shrugged and gave up after concluding, as you did, that it didn’t seem negative…
This is Stack Exchange on sentence-ending じゃあ, and they sound pretty authoritative…
OK, I can’t focus at the moment to try to apply that to these sentences. sigh!
I think they said that じゃ is always short for じゃない (when it’s where that might have been), and that broke my brain at the moment! 
PLUS my friend who is teaching English in Japan mentioned a school-kid language trend of ending things with じゃん (really loud) (are Japanese starting to do “sarcasm”?) (in the’80s, we would say something and then after a reaction began, say not!)
You did REALLY GREAT on your interpretations, CherryAppleさん 
I feel like a LOT of people (1) do not try to restate what they read in English and (2) do not try to understand every single word and every single particle. They just go “Uh huh…I think I get the gist” and keep blasting through content.
Me, I like breaking it down, because someday, I want to speak naturally in Japanese… So I feel like I need to understand the choices of including a sound (particle, word, conjugation, formality level, ai yi yi!!)… I call that “intensive Japanese study”, and do some every month, but not a whole lot… It’s exhaustingねぇぇ
I felt like maybe that sentence-beginning で is a casually-shortened version of では (“Well…”)