Doesn't holden contemplating suicide signify that he lacks dignity, morality, and courage?
Absolutely not; Holden, at that part in the novel, actually made one of the most courageous decisions in the novel. Salinger, as Holdem states:
"What I really felt like, though, was committing suicide. I felt like jumping out the window. I probably would've done it too, if I'd been sure somebody'd cover me up as soon as I landed. I didn't want a bunch of stupid rubbernecks looking at me when I was all gory (Salinger, 104)."
Here, Holden explains he opted not to kill himself by leaping out of his hotel window because other people would witness his mangled corpse splattered on the concrete pavement. Ironically, Holden exemplifies dignity here because he understands that traumatizing somebody outweighs selfishly taking the cowards way out of life, hence courage too. Likewise, he understands it's moral to keep pushing on in life, even when the worst seems to have arrived.
How is courage the most vital factor in determining one's success?
Isn't it obvious? With possession of value for one's integrity in their professional field of career, the final piece of the puzzle is see whether or not that individual can own up to themselves, and the difficulties they'll inevitably face in their future, especially when inconvenient for themselves.