The analyses of a text #4

The narrator recalls his adolescence.
He is an apprentice for the lawyer Mr. Spenlow.
He is now learn shorthand.

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I bought an approved scheme of the noble art and mystery of stenography (which cost me ten and sixpence); and plunged into a sea of perplexity that brought me, in a few weeks, to the confines of distraction. The changes that were rung upon dots, which in such a position meant such a thing, and in such another position something else, entirely different; the wonderful vagaries that were played by circles; the unaccountable consequences that resulted from marks like flies' legs; the tremendous effects of a curve in a wrong place; not only troubled my waking hours, but reappeared before me in my sleep. When I had groped my way, blindly, through these difficulties, and had mastered the alphabet, which was an Egyptian Temple in itself, there then appeared a procession of new horrors, called arbitrary characters; the most despotic characters I have ever known; who insisted, for instance, that a thing like the beginning of a cobweb, meant expectation, and that a pen-and-ink sky-rocket, stood for disadvantageous. When I had fixed these wretches in my mind, I found that they had driven everything else out of it; then, beginning again, I forgot them; while I was picking them up, I dropped the other fragments of the system; in short, it was almost heart-breaking.
[David Copperfield by Charles Dickens]
1. I'd like to know if the noun phrases in blue are the subject of "troubled."
2. I'd like to know if "who" refers to people.
3. I'd like to know what "a thing meant expectation."
4. And I'd like to know what "a pen-and-ink sky-rocket stood for disadvantageous." means.
Thank you in advance for your help.