Hi, Райля Салихова!
Looking only at the grammar, this is almost correct. The only grammatical mistake is that the last sentence should be: "Surely, he was a decent and generous guy" (with an "a" included).
However, I'm fairly confident that "the" should not be in the second sentence. Instead, it ought to be: "Indeed, he didn't assume to Mr. Farraday that he was omniscient" (notice the change in spelling of the last word). The only reason to include "the" is if the narrator does not know who Mr. Farraday is.
I hope my answer helps. Please let me know if you have any more questions.