The story strands in Little Dorrit

As Barbara Hardy wrote in her The Appropriate Form: An Essay on the Novel, “Henry James is almost always telling a single story, while Dickens and George Eliot and Tolstoy are telling several.” 
Middlemarch for example has 3 main plots (Dorothea- Casaubon- Will, Lydgate- Rosamond, and Fred- Mary). Anna Karenina has 2 main strands of story (the Anna one and the Levin one), each of which is expansive, complex, and populated with lots of different characters. War and Peace doesn’t have clearly separate strands, but tells the story of 5 families—the Bezukhovs, the Bolkonskys, the Rostovs, the Kuragins, the Drubetskoys, and a bunch of other characters. 
So how many story strands are there in Little Dorrit? 
I think there are 4: 
1/ The Marshalsea prison: Little Dorrit (Amy), her father William Dorrit, her sister Fanny, her brother Tip, her uncle Frederick, the turnkey… 
Dickens writes about the pride of the poor, which reminds me of Great Expectations. Amy is the main character, but the one who interests me more in terms of psychology is William Dorrit—as the Father of the Marshalsea, he lives in his own bubble, he lives in delusion and denial. Amy knows well that after many long years, her father cannot survive outside the prison—there is nothing he can do, and outside he doesn’t get the respect and reverence he has within Marshalsea. 
2/ The Clennams: Arthur Clennam, his mother Mrs Clennam, her servants Mr and Mrs Flintwinch… Amy Dorrit is also in this plot because she works there as a seamstress. 
3/ The bureaucrats—the term I use collectively for the Barnacles and the Meagles. Tite Barnacle is William Dorrit’s main creditor. The Meagles family meet Arthur during their Marseilles trip—they are Mr and Mrs Meagles, their daughter Pet (Minnie), and Pet has a maid called Tattycoram (real name Harriet Beadle). Tite Barnacle and Mr Meagles both work at the Circumlocution Office. 
4/ The Marseilles prisoners: Monsieur Rigaud (alias Lagnier) and John Baptist Cavalletto. In chapter 13, Cavalletto has an accident and Arthur Clennam sees him, but for the time being, I don’t know how they relate to other characters and the rest of the story.
In short, Little Dorrit has an intricate plot, packed with numerous characters. I would say the main character is Arthur Clennam because Dickens follows him more than other characters and he’s present in all 4 strands. Amy Dorrit is the 2nd main character. 
I am now on chapter 18, and Dickens makes everything more complicated by writing that Arthur Clennam considers marrying Minnie Meagles (Pet), and introducing Amy Dorrit’s lover John Chivery, son of a turnkey.  
This is such a good line: 

“In this affair, as in every other, Little Dorrit herself was the last person considered.” (B.1, ch.18)