There is world PvP. With the world population being so low, and the world size being so large it's pretty rare. There's also a lot of ways to avoid it, but whenever you're outside your own base it's always a risk. If you play smart, it's almost always possible to get away from a player, even if they're very highly geared. Most clans are pretty insular, a group of friends who have been playing for a long time. I've never joined a clan, personally, so I have no idea what they're like.