What should we cover when discussing parenting before our baby arrives?

Sharing of care. Many questions will come up! breast or bottle and how can your partner best help? Thoughts on future discipline, even issues of faith are assumed until friction arises.What does your partner believe about work and sharing of responsibilities both at home and about work. Sharing and listening will build the strongest relationship.
Not everything. You should talk together about all the things that concern you but mostly to get in the habit of talking about things in that way. When the baby arrives you'll find that there are all kinds of surprising and wonderful things that you never could have thought of in advance and that some things you worry about now don't happened. For now, the main goal is to learn to talk to one another!