Navmesh is used in order for AI to walk around the map. But yes, he does use a set path. In his blueprint, he selects one of four paths to take when he spawns to make it a bit unpredictable.
Technically, no. But I did follow some tutorials to learn how some things work, like how the "Spawn AI From Class" node works. but they were multiple ones and I learned certain things from posting discussions about how this works or how to do this to make this happen sort of thing. What I recommend you do, is just work on your games, and once you encounter a problem, look up a video or post a discussion on the unreal engine forums.