The analyses of a text #3

The narrator recalls his adolescence.
He came to the local lawyer, Mr. Wickfield' house, which he boarded at as he went to a school, after a long time.
Mr. Wickfield's only daughter Agnes is his best friend and counselor.
Mr. Wickfield's partner Uriah Heep and his mother live with Mr. Wickfiled in Mr. Wickfiled's.
Uriah Heep had confided to the narrator that he was crazy for Agnes in London.
When the narrator had a walk, Uriah followed him, and a skirmish ensued.

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'Before we leave the subject, you ought to understand,' said I, breaking a pretty long silence, 'that I believe Agnes Wickfield to be as far above you, and as far removed from all your aspirations, as that moon herself!'
'Peaceful! Ain't she!' said Uriah. 'Very! Now confess, Master Copperfield, that you haven't liked me quite as I have liked you. All along you've thought me too umble now, I shouldn't wonder?'
'I am not fond of professions of humility,' I returned, 'or professions of anything else.' 'There now!' said Uriah, looking flabby and lead-coloured in the moonlight. 'Didn't I know it! But how little you think of the rightful umbleness of a person in my station, Master Copperfield! Father and me was both brought up at a foundation school for boys; and mother, she was likewise brought up at a public, sort of charitable, establishment. They taught us all a deal of umbleness - not much else that I know of, from morning to night. We was to be umble to this person, and umble to that; and to pull off our caps here, and to make bows there; and always to know our place, and abase ourselves before our betters. And we had such a lot of betters! Father got the monitor-medal by being umble. So did I. Father got made a sexton by being umble. He had the character, among the gentlefolks, of being such a well-behaved man, that they were determined to bring him in. "Be umble, Uriah," says father to me, "and you'll get on. It was what was always being dinned into you and me at school; it's what goes down best. Be umble," says father, "and you'll do!" And really it ain't done bad!'
[David Copperfield by Charles Dickens]
1. I'd like to know what "now, I shouldn't wonder?" means.
2. I'd like to know what "There now!" means.
3. I'd like to know what "it" refers to in "Didn't know it!".
4. And I'd like to know "it" refers to "what goes down."
Thank you in advance for your help.