The analyses of a text #1

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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'"My charges against - HEEP,"' he read on, glancing at him, and drawing the ruler into a convenient position under his left arm, in case of need, '"are as follows."'
We all held our breath, I think. I am sure Uriah held his.
'"First,"' said Mr. Micawber, '"When Mr. W.'s faculties and memory for business became, through causes into which it is not necessary or expedient for me to enter, weakened and confused, - HEEP - designedly perplexed and complicated the whole of the official transactions. When Mr. W. was least fit to enter on business, - HEEP was always at hand to force him to enter on it. He obtained Mr. W.'s signature under such circumstances to documents of importance, representing them to be other documents of no importance. He induced Mr. W. to empower him to draw out, thus, one particular sum of trust-money, amounting to twelve six fourteen, two and nine, and employed it to meet pretended business charges and deficiencies which were either already provided for, or had never really existed. He gave this proceeding, throughout, the appearance of having originated in Mr. W.'s own dishonest intention, and of having been accomplished by Mr. W.'s own dishonest act; and has used it, ever since, to torture and constrain him."'
'You shall prove this, you Copperfield!' said Uriah, with a threatening shake of the head. 'All in good time!'
'Ask - HEEP - Mr. Traddles, who lived in his house after him,' said Mr. Micawber, breaking off from the letter; 'will you?'
'The fool himself- and lives there now,' said Uriah, disdainfully.
[David Copperfield by Charles Dickens]
1. I'd like to know what "through" adverbial phrase qualifies.
2. I'd like to know what "at hand" means here.
3. I'd like to know what "represent something to be something" means.
4. And I'd like to know "it is" implied before "the fool himself."
Thank you in advance for your help.