Paradise Lost is eluded to on p. 273 - in which it is declared that the "world lay before her." Paradise Lost is a poem written by John Milton. It is a biblical story about Adam and Eve's expulsion from the Garden of Eden. It is an allusion to a religious worldview, but this book is thoroughly secular. However, Henry James seems to be posing the question of moral problems from this secular perspective in terms similar to ones that reference biblical interpretation. Is there really such a thing as evil in the world?
The Married Women's Property Act of 1882 was passed in England around the time that James wrote this novel. This law allowed for women to some property in their own right. It allowed for them to take the first steps towards establishing a legal identity. However, when the novel takes place, this act was certainly not in effect. James' decision to set the novel during the 1870s allows for him to explore the conditions leading up to the act.
The name of the Touchetts' house, Gardencourt, is an allusion to George Eliot's Grandcourt in Daniel Deronda. Grandcourt is a terrible place in Eliot's book, whereas Gardencourt offers a more hopeful vision of women's opportunities.
The preface alludes to Shakespeare's Much Ado About Nothing in talking about how the novel is a form that makes "ado about something." Perhaps James is suggesting that there is really nothing to Isabel Archer in herself to make her interesting - there is just the fact that people make such "ado" about her that makes her into "something" rather than "nothing."