I had to cut down the original question text, as there were multiple questions present. They are all real interesting and I encourage you to repost them separately. In my mind, I think that Lennie and Curley's wife being along at the start of Chapter 5 is significant because it brings together two fairly sad creatures in one instant. Lennie's hopes of a life where he can "tend the rabbits" and be surrounding with creature that allow him to enjoy a state of being in the world are set against Curley's wife's dream of being in "pitchers" and being someone of importance and significance. In this particular instant, the striking similarity of their dreams and their own potential for loneliness because of their dreams' denial is brought out in full force. At the same time, the differences between them is also present in that Lennie does not possess bitterness about the deferral of his dreams. Perhaps, this is because he lacks the capacity for it. Yet, Curley's wife is bitter and she is distraught that her own dreams were not recognized. I think that another significant difference that is evoked in chapter 5 is how Curley's wife lives her life with the consciousness of her dreams being negated, while Lennie possesses the childhood innocence that at some point, in some way, his dreams can be fulfilled. The moment where both of them interact through touch is one where neither one understands the vulnerability of the other, and where Steinbeck might be asserting that the cost of the denial of our dreams could be our ability to understand another person's own pain when they experience what we have.
they are both similar in being treated differently. Lennie is treated differently just because of his mentality and Curley's wife istreated differently because of her gender. she is the only woman on the ranch. Lennie dreamt of having a farm ( just to tendthe rabbits ) and Curley's wife had a dream of becoming a movie star. Both their dreams didint come true. A differnece is that Lennie has George always by his side while Curley's wife has no one (her husbandis always out )