The issue is, regarding discipline - you need to be consistent. And you need to NOT do anything that isn't working or that you can't follow through with. Ignore bad behaviour rather than half-heartedly correct it then drop any consequence. At least if you're ignoring it, you're sending the message of, "I'm not dealing with this right now; nor am I acknowledging it." of course you can't go on that way, but unless you can follow through, don't start anything. Or you make the problems ten times worse. Fast.
He sounds like a bright kid. He also sounds very frustrated, but a lot of things (including physical limitations). As a starting point, don't punish the behaviour borne of frustration. ignore it. Move him somewhere safe and ignore him. He might threaten to hurt himself but if you remove anything he can use to injure himself with, then walk away and leave him until he calms down, you might get better results. If he STILL hurts himself and does real damage, take him to the hospital. That is not good. But I'm betting he's attention-seeking and not serious about the threatened self-harm (although you may feel I'm wrong, and I could be - trust your instincts, please). Generally, a smart kid who is merely frustrated, won't do himself serious harm deliberately.
If holding him makes him worse, don't do it. It may be great for some, but not for others. You find what works and do it. You stop doing what doesn't work. It's as simple as that.
it's not a perfect answer but it's a start. All you can do is make a start. To think of anything else is just too overwhelming.
He seems to respond well to academic stimulation - give him more. Throw more at him as long as he can handle it. Challenge him with puzzles, complex problems, whatever you feel will help him develop.
I know how you feel about not letting anyone else watch him - we were repeatedly offered respite for difficult child 3 but I could never bring myself to take it up. Respite is great if you can use it but not all of us can.
Turn off your guilt. It's a waste of energy. Turn off feeling bad that he will never be normal - what is normal, anyway? All this is slowing you down and putting up a barrier for you. He may be sensing this and resenting what he may feel is your pity. Also, don't talk about any of this in front of him or where there is any possibility of it being in his hearing. Our kids are always smarter than we think. They are also VERY quick to take on their own personal burden of guilt and inadequacy.
Instead, teach him that he can do anything he puts his mind to. A book I would recommend (try and find it in the library) is "I Can Jump Puddles" by Alan Marshall. it's an old Aussie book but a darned good one. Marshall was an author who contracted polio when he was a young boy. This changed his life as his plans to be a horse breaker like his father, had to go. He would never ride a horse, let alone be able to break one. ALL his knowledge counted for nothing. Or so they thought.
It's an entertaining, uplifting read about living with people trying to protect you, but still trying to be a 'normal' boy. It has been made into a mini-series starring Adam Garnett and later Lewis Fitzgerald as Alan - the mini-series may only be available in Australia; and a movie was made in Czechoslovakia, of all places. All are entertaining - the book, the film and the mini-series. And all are very different but the message is the same - when you see t he boy not only riding the horse but jumping it, you can only marvel at the stubbornness and glory of the human spirit.
A man I met at a major charity fundraising committee has cerebral palsy. He is hard to understand sometimes, when he speaks. But when he speaks the room goes quiet because he is ALWAYS worth listening to. He has difficulty walking but holds down a very senior position as an accountant - he was actually the treasurer for our state combined charities committee. Very respected - I later saw him interviewed on TV about something to do with accounting. An amazing man, a sharp wit and someone clearly who's found his niche in life.
We have another bloke in Australia with cerebral palsy - he's a stand-up comic. A rebel, always the difficult kid, he admits to having been a big behaviour problem. His stage name is Steady Eddie. Also someone whose CDs would be worth tracking down.
I tell you this not so you can share this with your son, but so YOU can feel positive and not negative. If your son wants to go climb a tree, let him. Don't help him unless he asks for it.
Our neighbour's son had a near-drowning incident which left him with severe cerebral palsy. Her son was a year older than difficult child 3. At the time I could see the problems she was living with, but I could also see the different problems difficult child 3 had. Although her son was non-verbal and for a long time had lost any English he had learned he would respond to me if I said ANYTHING in Spanish, even the 'count to 10' which is all I can do. I could see his eyes intently on my face, encouraging me to keep trying. At the time he was a physical wreck who people said should have been allowed to die. He had no controlled movement of his own at all; no swallowing; his eyes would roll up into his head at first; he was completely dependent.
They moved away some years ago but last I heard he was learning via a computer, using it communicate, was eating and drinking normally and learning to walk (a Hart walker). And, of course, still bilingual. He could move himself around on the floor and would get himself up onto his knees. His parents keep saying, "He can do whatever he wants - he is already doing more than they ever said he would." I know that if he indicated he wanted to climb a tree, his father would climb it with him.
You don't have to be Supermum. Just mum. Your aim is for him to be happy, productive and independent. He's got a few obstacles to this and will need your help in finding ways around them, but he can do it. He's already on the way.
The bad behaviour you see, the frustration - it's a very healthy sign. he's fighting. It's far better than if he was just giving up.
All you can do is help him deal with it productively and channel it.
He is not a normal child. You need to think (and operate) outside the square. We all do. It sounds like you've already begun to do this. Have faith in yourself, your feelings and your decisions. And have faith in him also.