7 yr old not able to follow instructions immediately

My 7 yr old son has a lot of trouble with the 5 steps of 'Following Instructions'.
He doesn't seem able to look at the person, for more than 1 to 2 seconds.
He is unable to stand still at anytime in his life.
He doesn't seem to be able to do the task immediately so he asks to disagree appropriately EVERY time, even if he just asks for 2 more minutes to keep doing what he was doing.
He has a reason for not doing everything and he really falls apart if I give him a 'NO answer'.

He is unable to stay calm almost any time of his life.

He chews anything hard e.g. plastic plates and cups, wooden toys, pencils, zippers, toy animals, Lego etc. He says he has to, and "it just feels good to bite something hard".

Apparently he is unable to control his bladder. He wets himself anywhere from 3-6 times a day. This makes a lot of laundry. He doesn't always know that he has wet.

I'm not really sure what my question is, but I feel I need to understand him and I don't.

If you could enlighten me with any thing you know I would be very grateful. I get especially frustrated with his non stop 'disagree appropriately' and NEVER just an OK.