I am by no means an expert, but this whole being scared of you thing sounds to me like he´s upset with you. You were after all the person who took him from his last home, he may see you as that person that took him away. I had a bunny once that her mate died and I took him out, but because it was me who took him out I couldnt get within 10 feet of her cage without her losing it and growling. she got over this once I found her a new friend (mate), all my bunnies are fixed.
Give him time, I know its hard. Ive got 2 conures that were very badly mistreated and are terrified of all people. Ive had them about 6 months now, and they still run from me when I open the cage. They will sit with me once they are out though, until they see the opportunity to ditch me for my other birds company.
Encourage the good behaviors, and never use his name if he´s doing something you dont like. ¨NO¨ works better, otherwise everytime you say their name he may think hes done something wrong. Also try giving him a mist in the morning, cockatoos bathe right when they wake up by nature, it also calms them down. Ive also been told by my local exotic bird rescue to offer very diluted camomille tea, mist him with it and as he preens his feathers it will calm him down.
Your doing great and he secretly loves you trust me. Ive got one that acts the same way, but does he ever get mad at me when I go away for a couple days.