What do I need to do now to help to ensure I have physical custody of the child once born?

If we are talking about a fetus conceived in Wisconsin, there is not much you can do until the child is born. Sadly, we all know that a certain number of pregnancies end in miscarriage, or planned abortion. So I do not think you need to notify the apparent biological father. Once the child is born, and very soon after that, I suggest you consult a lawyer in the state to which you are moving about its requirements. You probably should still be able to begin a paternity action, have the father ordered to pay child support, and provide for periods of temporary placement (formerly 'visitation') with him, if he wants it.