That face bite may well have been when the bird was wound up over someone or something else in the room. My worst amazon bites have come from the dog sticking her nose to close, another bird making the bird that was on me mad. Some amazons are very reactive to other people. So, instead of biting the person they really hate, they will bite the person they are on because its quicker. If he loves you, but hates someone else that is around often, be very careful with him when that other person is around. Sometimes its almost a reflexive action. Hated person walks in the room, bird instantly bites the favorite person they are sitting on. Just like that, with not enough warning to get the bird off the shoulder. Or you turn your head to the side when you see the other person walk in so at least they can't get your face but your hand gets it when you try to get him off your shoulder before your face gets bit. Sometimes no matter what you do, your going to take a bite when you have an amazon like that. You easily figure out what the bird's triggers are and learn to avoid them. But until then, if he has a history like that, I'd be a little careful with him. Even though it certainly seems he is in love. Its slightly unusual to have an amazon that snugly. And it seems like its usually older birds. But, as much as they love you, they can have an equally violent reaction if the right trigger is present.
Tough love tends to do the trick with amazons and diet. My older female came to me with a nasty vitamin A deficiency and her owners claimed that despite their best efforts, she would only eat seed. Two weeks later she was eating all the good stuff. I did just what you are doing, restricted the seed and let her have her choice of anything else nutritious. I loaded her bowl with sweet potato, veggies and pellets but no seed except a very little bit at night. 2 days of screaming and pacing and she was converted.
He is a nice looking bird. You might want to monitor the bottoms of his feet. In the video it looks like he has a couple dark spots on the bottom of one foot. That could be the beginnings of a problem.