Do you know much about cockatoo body language? I often forget how little I knew in the beginning and that whats obvious now to me may not be for a newbie. How they hold their feathers can tell you a lot about how they are feeling. The way you mentioned him hitting his beak of things make me think of it.
True striking of the beak is a warning that a bite might be coming. My cockatiel use to do and i have seen other species of parrots to it too. I don't think I've ever seen either of my cockatoos do it thou. They will hiss and puffed out their feathers when they feel threatened by something.
Beak clicking is a extremely common in cockatoos. Soft clicking is a very good sign, i take it to mean "I want to be friendly with you" or "I mean you no harm" Here's an example of what I'm talking about
Cockatoos often do in confine spaces too, like under a blanket or something.
Occasionally cockatoos can do hard clicking which is usually a warning and a sign something it aggravating them. Now it doesn't always mean this. Zane my M2 would do hard clicking when he was happy or mad. I think it was something he learn in captivity. Since birds in captivity aren't in a natural environment, unnatural behaviours can arise for that. So its important to remember this is just guide and your bird may act differently depending on how he has learned to interact with people.
Feather beards are a sign of being content or relaxed. Here's a picture of Echo with a feather beard
Basically its when his facial feathers cover his lower beak.
In my experience rised Crestes mean a variety of things. But mainly its a sign of alertness, whether it curiosity or supprised or just general interest in something.
Beak grinding usually means they tired but content
Those are just a few obvious signs I could think of. When you get to know your more you'll learn his mannerisms and what's unique to his personality