What do we owe future generations?

We all have clear intuitions about our moral relations to people who did, do, and will exists. But what about people who could exist? Are we obligated to create them because we can? If so, how many? How do we weigh our own needs and wants against theirs? Is it more important to create good lives for these people or to create as many as possible? What does this look like as policy? Should we be offering tax incentives, or embark on engineering projects to increase the carrying capacity of our universe?