All of this guy's comics are awesome. It's too bad they can get so damn confusing. If I made any mistakes in translating, don't hesitate to point them out.

Yes, they're great. I think you've done a pretty good job translating this one, too! But let's check it anyway:
- In the first panel, I'd leave the literal "I could die".
- In the second panel, where are you getting "making that look"?
- In the next balloon, I think それマジだし means that they were in fact hired thanks to their connections (so, something like "But that's true." instead of "That's true, but...").
- I don't know the context of the series, but ティアナに教える事無くて困る sounds more like "It's bugging me that I/we have nothing to teach Teana" to me.
- There's a pun there, where Teana's やる気マンマン turns into ヤリマンマン for Nanoha. ヤリマン means slut or nymphomaniac. I guess this could be rendered with a double-entendre in English.
- I think the fourth balloon is more like "If you say any more I'll throw you into an asylum". ぶち込む is transitive, I don't think it can mean "forcing oneself in" (not without something like 身を, at least). Besides, it'd have to be past tense if it was referring to their entering the... wherever they're working at.
- Third panel: そんな話じゃなくて sounds more like "That's not what I'm talking about". (Leaving "I could die" in the first panel also keeps the ambiguity.)
- gachi should be elegance or good taste... but perhaps it has a slang meaning? This is also relevant to the title.
- In the eigth panel, 迷惑かかる is "causing trouble" to Yuuno, not making him suspicious.
- In the ninth panel, もう死んでるっしょー腐ってるっしょー means "he's probably already dead... he must be rotting".

...ok, that was a bit longer than I thought it'd be. Well, Nakayama's comics often have many interesting language points.

As usual, most every suggestion you made is probably right. However, I am fairly sure that ガチ in this case is internet shorthand for ガチンコ (going all out), rather than 雅致.

Fate looks so yandere. It's kind of hot.