Huck steals things but doesn't feel too bad because he "intends" to give it back. Huck lives by a social code that does not conform with Southern manners. Huck's close friendship with Jim is positive aspect of this. Huck does feel bad for leaving the two robbers and tied up man on the sinking ship. This doesn't make Huck a hero. I think he is honourable in his own way. He is certainly developing his sense of honour at this point in the novel. Huck rejects Southern social mores of bigotry for a more enlightened view of humanity. In the end, Huck stays loyal to Jim. Huck is even suspect of his friend, Tom Sawyer, and his motivations for rescuing Jim
The irony of the story relies on the principle that nothing is truly perfect in life. It was not the fire that directly disabled Rochester but the events that surrounded the people who were in that fire which caused Rochester to lose his eyesight and one of his hands. This was not entirely a bad experience because it ultimately brought him back to Jane.
An interlude can really take on any emotion that you wish for it, but if you have to choose between one of these option then I suppose the best is "somber"