I have had to edit down your question to only include one question, according to enotes regulations. This is a great question! One of the things that is really important to focus on in this novel is how the relationship between Jim and Huck changes as the novel progresses and Huck matures more and more. One of the key themes of the novel is the coming of age of Huck, and this is exhibited through his increasing understanding of the wrongness in slavery and his increasing affection for Jim.
It is certain, however, that from Huck's discovery of Jim on Jackson's Island with him, Jim plays an almost fatherly role - he is the voice of reason in Chapter 9, acting sensibly to hide and protect their belongings from the rain and the potential of men coming to look for them. He also, in the same chapter, prevents Huck from looking at the dead man they find to spare Huck's feelings (we later find out that it is Huck's father). Likewise, as the novel progresses, we see that Jim cares so much for Huck that he often takes Huck's shift at keeping watch at night, allowing Huck to sleep. From Chapter 15 and the trick that Huck plays on Jim, convincing him that they were not separated by the fog, it is clear that Jim feels very deeply for Huck:
"When I got all wore out wid work, en wid de callin' for you, enn went to sleep, my heart wuz mos' broke bekase you wuz los', en I didn' k'yer no' mo' what become er me en de raf'.En when I wake up en fine you back agin, all safe en soun', de tears come, en I could a got down on my knees en kiss yo' foot, I's so thankful."
This love and affection so shames Huck that he says:
It was fifteen minutes before I could work myself up to go and humble myself to a nigger; but I done it, and I warn't every sorry for it afterwards, neither.
This is one example of Huck's maturing as he realises that "niggers" are people too and it is wrong and cruel to play tricks on them.
Thus, I would say that during Huck and Jim's voyage down the river, more and more their relationship develops into a kind of a father-son role as Jim cares for and looks after Huck and Huck becomes more and more aware of his love for Jim and how he is so self-sacrificial.