1.Here what you need for the animation idle walking run(ep 7) it’s quite simple: BP 3rd Person Game: Introduction | 01 | v4.8 Tutorial Series | Unreal Engine - YouTube
2.AI code only needs to be in AI Behaviour Tree(or at least talking with it) anything else is bad code at best and game crushing at worst(such as placing AI into tick) its not so hard to find a random point from actor check if he can go there and then send him there.
3.You just need an actor generator, many ways to do it but as I see it you need it with volume(more like just a box) get the box dimensions and spawn inside it from actor array that you created, random numbers from random int. Good luck.