I am only allowed to respond to one question, and so I have edited your question accordingly to focus on complications in the plot of this excellent short story. Please remember that you are not permitted to ask multiple questions on enotes.
When we think of the complications, or the rising action of the tale that leads to the climax, the biggest struggle that Bella faces is certainly the poverty that she and Jim live in and how it forces them to cope with severely reduced circumstances. Note how this is a fact that is emphasised from the very beginning of the story through repetition:
One dollar and eighty-seven cents. That was all. And sixty cents of it was in pennies. Pennies saved one and two at a time by bulldozing the grocer and the vegetable man and the butcher until on'e cheeks burned with the silent imputation of parsimony that such close dealing implied. Three times Della counted it. one dollar and eighty-seven cents.
Her inability to save enough money to buy a present that is representative of her love for her husband and her struggle to finally buy what she wants as a present for Jim represent the complications of the tale. First she is confronted with her poverty, secondly, she needs to make the sacrifice of her hair to gain the money to buy the present for Jim, thirdly, Della receives the combs as a present, fourthly she gives Jim his present, and lastly, she discovers what he has sold to buy Della her combs.