If I have to pour concrete over a large area (8 cubic yards) can I pour it in sections or does it have to be all at once?

You can pour it in sections.

You can pour it in sections but If a section has hardened before you pour an adjacent section the area where the two meet is called a "cold joint". I always use some kind of expansion material to make a clean edge with less potential for cracking and buckling between the two. Your geographical location (weather, wetness, etc.) may help to determine what material to use. Lots of folks use 2X4 pressure treated forms that they leave in place after they pour a section and it'll provide your first form for the next section. Felt expansion material is also used. Redwood will work also. Good luck!