and I suppose the antagonists would ideally be the opposite to that, for maximum character conflict? They need to be a hurdle somehow, and if they're actively pursuing the opposite of the protag's goal, the motivation should follow from there.

From what I've read, it often works well if the antagonist and the protagonist have the same goal -- then the antagonist can also act as a foil and raise the stakes for the protag. Like how in Guardian, everyone's after the Hallows. (I think I got this from Take Off Your Pants!: Outline Your Books for Faster, Better Writing by Libbie Hawker, FWIW.)