Quote 4
"The head of the firm did suggest to me this morning a possible explanation for your tardiness – it concerned the cash payments recently entrusted to you – but really, I practically gave my word of honor that this explanation could not be right" (1.19)
In addition to possible sexual deviance in Quote #1, Quote #2 suggests that Gregor may be guilty of misconduct at his firm. We never find out what really happened to those cash payments, although Gregor insists that he's done nothing irregular.
Quote 5
"Look how these roomers are gorging themselves, and I'm dying!" (3.11)
Here we have another reference to Gregor as "dying." The passage draws a contrast between the human roomers and Gregor in order to ask the reader whether it's OK to maintain human life over an insect's, even if the insect is your erstwhile son/brother.
Quote 6
That's all I'd have to try with my boss; I'd be fired on the spot. Anyway, who knows if that wouldn't be a very good thing for me. If I didn't hold back for my parents' sake, I would have quit long ago. (1.5)
The "that" that Gregor is referring to here is waking up late like the other traveling salesmen. Ironically, that's just what he's doing here, although we don't find out he's late until the next paragraph. Of course, he has a very good reason to be late – he's a vermin. But the transformation has the unintended consequence of fulfilling Gregor's wish to be rid of his job.