I think most of these questions will be answered shortly, if you are patient. I'm not fond of Wickham as a character, and mostly these days I try to find ways to circumvent that story line altogether. You'll see him, but not a whole lot of him.
I don't know that I deliberately decide to leave out other characters, I just don't think about them very much. This story kept getting longer at the end because I kept remembering "oh yeah, I should probably talk about her," and "oh yeah, I need to put in something about them." I write what I like, and hope others like it too.