The analyses of a text #2

The narrator recalls his adolescence.
He is beginning a new life as an apprentice in Doctors' Commons at London.
The narrator's best friend Steerforth and his Oxford friends came over to the narrator's apartment to dinner.
After dinner and much drinking of wine, they went to a theatre, where he encountered his old friend Agnes and she advised that he had better go home?I think she found him so very drunk.
He awakened with much remorse the next day.
And he visited Agnes's lodging at her invitation after work.

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"It is very bold in me," said Agnes, looking up again, "who have lived in such seclusion, and can know so little of the world, to give you my advice so confidently, or even to have this opinion. But I know in what it is engendered, Tritwood, in how true a remembrance of our having grown up together, and in how true an interest in all relating to you. It is that which makes me bold. I am certain that what I say is right. I am quite sure it is. I feel as if it were someone else speaking to you, and not I, when I when I caution you that you have made a dangerous friend."
[David Copperfield by Charles Dickens]
1. I'd like to know why it is "in," not "of."
2. I'd like to know why it is "is engendered," not "engendered."
3. I'd like to know "it is" implied after two "in how true"s.
4. I think it refers to "speaking to you."
So I was wondering if it is possible that "to speaking to you" is in apposition to "someone."
5. I'd like to know if "it were" is implied before "not I."
Thank you in advance for your help.