The analyses of a text #3

The narrator recalls his adolescence.
He, his great aunt Miss Trotwood and his friends came to Ham's office to meet Mr. Micawber who is the clerk for local lawyer Uriah Hip, whom he struck in the cheek because of his mean behavior.
Uriah Hip is the partner of Mr. Wickfield, who is very sick now, whose only daughter Agnes is narrator's old friend, whom Uriah Hip has an affection for.
Now Mr. Micawber is exposing Uriah Heep having done evil deeds, reading a prepared letter.
"Mr. W" refers to Mr. Wickfield.
Mr. Micawber have lived since Uria Hip and his mother moved in with Mr. Wickfield.

Chapter 52 I ASSIST AT AN EXPLOSION

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Mr. Micawber read on, almost smacking his lips:
'"To wit, in manner following, that is to say. Mr. W. being infirm, and it being within the bounds of probability that his decease might lead to some discoveries, and to the downfall of - HEEP'S - power over the W. family, - as I, Wilkins Micawber, the undersigned, assume - unless the filial affection of his daughter could be secretly influenced from allowing any investigation of the partnership affairs to be ever made, the said - HEEP - deemed it expedient to have a bond ready by him, as from Mr. W., for the before-mentioned sum of twelve six fourteen, two and nine, with interest, stated therein to have been advanced by - HEEP - to Mr. W. to save Mr. W. from dishonour; though really the sum was never advanced by him, and has long been replaced. The signatures to this instrument purporting to be executed by Mr. W. and attested by Wilkins Micawber, are forgeries by - HEEP. I have, in my possession, in his hand and pocket-book, several similar imitations of Mr. W.'s signature, here and there defaced by fire, but legible to anyone. I never attested any such document. And I have the document itself, in my possession."' Uriah Heep, with a start, took out of his pocket a bunch of keys, and opened a certain drawer; then, suddenly bethought himself of what he was about, and turned again towards us, without looking in it.
'"And I have the document,"' Mr. Micawber read again, looking about as if it were the text of a sermon, '"in my possession, - that is to say, I had, early this morning, when this was written, but have since relinquished it to Mr. Traddles."'
[David Copperfield by Charles Dickens]
1. I'd like to know what "it" refers to.
2. I'd like to know if both "for the before-mentioned sum" and "stated" modifies "a bond."
3. I'd like to know what "was advanced" means.
4. And I'd like to know if "in his hand and pocket-book" means "from his hand and pocket-book."
Thank you in advance for your help.