1) By dogmatic slumber, Kant meant that he was willing to rely on faith (dogma) and not really question his beliefs. What Hume did was try to explain morals and cause and effect based solely on reason. Hume argued that we have no basis for our concept of one cause having a certain effect, and infer that from our experience of the world. He also said that morals aren't based on reason, but our specific passions. Kant applies Hume's doubts to "a priori" knowledge, and thus to all metaphysics. Kant thus makes it his goal to define metaphysics (and eventually morals, in the "Grounding of the Metaphysics of Morals) based solely on reason.
2) When Kant refers to a Copernican revolution, he is referring to a shift in what we consider the center. Copernicus' famous conclusion was that the earth revolves around the sun, as supposed to the conventional wisdom of his day, which was that the sun revolves around the earth. Kant says that, up to him, it has been argued that knowledge must conform to objects. He points out that that way of looking at things has left people unable to get to further a priori truths. He suggests we might have more success in metaphysics if we assume that objects conform to knowledge.
In short, he identifies a world as we perceive it, ignoring the question of how the world might actually be, and begins his arguments from there.
3 + 4 to follow
This would agree better with what is desired, namely, that it should be possible to have knowledge of objects a priori, determining something in regard to them prior to their being given.
Immanuel Kant, The Critique of Pure Reason