(Because only one question can be asked at a time, your posting has been edited.)
It is ironic that Pip so eagerly moves to London in his desire to become a gentleman, for the atmosphere there is one of squalor, crowding, and corruption. When Pip first arrives in London and traverse the street towards the offices of Mr. Jaggers, he is stunned by the appearance of the place. The room is lighted by only a skylight; there is dust and grit and papers and other debris littering the floor. When Pip tells the clerk that he will "take a turn in the air," and goes outside, he is taken aback by the grim stone building known as Newgate Prison. The roadway near it is "covered with straw to deaden the noise of passing vehicles." Smells abound, especially of "spirits" and beer. Various unsavory types enter Mr. Jaggers's office while Pip waits for the unscrupulous barrister.
At his meager apartment where Pip goes to live with Herbert, there is a watchman who stands outside the building. The lodging in Barnard's Inn where he and Herbert are to live is described by Pip in his dismay,
the dingiest collection of shabby buildings ever squeezed together in a rank corner as a club for tomcats...a melancholy little square that looked...like a glant burying ground. I thought it had the most dismal trees in it, and the most dismal sparrows, and the most dismal cats, and the most dismal houses that I had ever seen. The windows of the houses were in every stage of dilapidated blind and curtain, crippled flowerpot, cracked glass, dusty decay, and miserable makeshift.
It is no wonder that Wemmick lives outside the city in his "Castle" with its drawbridge in a quaint little bucolic area where he has his fowls, and rabbits. Behind this area is a miniature fortress with his cannon that he sets off for his Aged Parent.
In contrast to the dingy, smelly, miserable squalor of London whose streets abound with thieves and unsavory types, the marsh with its sluices and dams, its wet grounds and its cows wear a "respectable air" as Pip has remarked upon leaving them. The forge with its warmth and the love of Joe within offers a haven for little Pip from the abuses of his sister. The marshes are spacious and although damp and foggy, they have the smell of nature about them, not the smell of urban squalor. Always there is love in the humble home of Joe.