What's the easiest way to get and play the right animations for npcs?

I added an AttackAnim <animNumber> to each npcdesc entry for each of the animations I wanted them to play out for combat. Then, in your hook, you can just read in their desc entry and get the AttackAnim entries to have them perform.

Other than that, to be easier, I believe most of them, possibly not all, use the attack actions for their attack animations, so you might be safe in just using those. I believe they are 0x4, 0x5, and 0x6. Just send those to the PerformAction() function to have the mob perform that animation.