Hi, and welcome. Crikey, your son sounds like a mixture of my two boys!
A few things that could help for now -
1) If you haven't already (or maybe even if you have, but a while ago) - organise a thorough neuropsychologist evaluation. people on this site can help you there more than I can, it's a bit different Down Under.
2) He sounds like he's dealing with sensory integration issues, body awareness issues, a need to control as much as he can around him (common in Pervasive Developmental Disorder (PDD) and ADHD) and really poor organisation skills. I'm also wondering - do his hands hurt if he tries to use a pen, or utensils, for any length of time? What is he like at colouring in? What is he like at using scissors? I ask this, because it can be a HUGE, and often unrecognised, issue.
Basically, with my younger three kids the problem is hypermobile joints (like double-jointedness). This is NOT a good thing, despite what we may have thought when we were growing up. For us it's especially bad in the boys, especially difficult child 3. His hands hurt when he holds a pen or pencil, as well as when he uses a knife & fork. We had him learning piano early, because it trains the hands to pull the fingers in, like claws, for best playing position. But unless he concentrates, his fingers splay out and when he pushes his fingers onto th keys his fingertips bend backwards. As a result, to hold utensils he has to force his muscles to grip tight, and they cramp really quickly.
It took an Occupational Therapist (OT) to confirm this diagnosis when he was about 3. And now we have an Occupational Therapist (OT) in the family - we can see it in the other two (although they were previously privately assessed and also found to be hypermobile).
With the label of hypermobility, we were able to get the kids permission to use a computer keyboard instead of having to hand-write. it's made writing tasks much easier.
I do wonder if hypermobility is connected to some sub-group of Pervasive Developmental Disorder (PDD), I keep coming across this connection.
3) The eating with hands thing, coupled with poor toilet hygiene - generally these kids are fairly fastidious, when they're reminded. At least about health. If you remind him that eating with hands requires hands to be scrupulously clean, he may be more willing to wash before eating. It could even begin setting the habit in place firmly. If you remind him that especially if he's not good at cleaning himself up yet, plus he prefers to eat with his fingers, he should make a point of washing his hands after using the toilet.
Something else I STRONGLY recommend - until he IS able to clean himself up better, get a refillable packet of wet wipes and keep them in the bathroom beside the toilet. Keep a bin in there for him to put the used wipes in (better than flushing). Get him to use the wipes AFTER using paper. The wipes are a much easier way of keeping himself clean. Failure to clean up properly will lead to sore, inflamed skin that will be really messy and painful. To treat this, use a wipe to make sure everything is spotless, then get him to anoint himself with oil of some sort - any cooking oil will do, frankly. A tiny amount will go a long way and provide a short-term barrier that will help his skin to heal. We use coconut oil or olive oil and keep a bottle handy in the loo. A small jar of coconut oil could be best for you, since it's solid except when very warm, but quickly melts on the skin. It would be less messy for him to manage. Or you.
4) Something that worked for me with difficult child 1, was I threatened to clean him up myself if he didn't get it right. If he forgot to wash his hair, I would offer to go into the bathroom and do it for him, while he was naked in the bath. he quickly got the hang of washing his hair, because he knew I WOULD walk in on him to scrub him down if he failed to do it.
5) His IEP should include consideration for his poor organisation skills and homework issues (this is more like my difficult child 1 (difficult child 3 is pretty good about organisation). basically, my difficult child 1 has HUGE problems holding more than one instruction in his head at a time. Things just have to be written down. He can't be judged by normal standards - he simply doesn't have the same tools. He's improved a vast amount now, mostly over the last few years. But if you try to discipline something he has poor control over, you will go backwards with him. The school should have taken this into account with his IEP.
6) With his IEP, you SHOULD have been part of the process. I hope you were. You have to be able to contribute and explain about his needs as well as have what you want for him taken on board by the school. It's not their place to tell you what they think he needs - they have to listen to you, and also to him where possible.
Sometimes it's really tough, especially if there is another adult in the picture who you feel is undermining your efforts.
So, a final suggestion - ignore his birthdate. Treat him as an exceptionally bright four year old. Don't expect the same standards of behaviour and coping ability from him as others do from their children of the same age. You won't get it. Don't even try. All you CAN get, is what he can give you. And that right now is going to be way behind his chronological age. But he IS bright. He needs mental stimulation. He also needs the things that make him feel secure and calm. He also needs your help and a LOT of support with personal organisation. You can't do it all. School stuff - the school should be doing it. If he fouls up at school, it's a school problem.
difficult child 1 was supposed to get his homework written down by the teacher (or aide) into his homework book. Or at the least, they were supposed to supervise him writing it in for himself. It was in his IEP. But then one teacher (a lot of them chose to ignore the IEP) handed out the homework on a torn off slip of paper (not even a whole sheet), without drawing attention to it by saying, "Here is your homework." Of course difficult child 1 forgot what he had in his hand and probably dropped it in the nearest bin. He was penalised for failing to turn in his homework, but I felt the teacher should have been penalised for failing to follow the IEP. What I kept getting from the school - "He's 13, he should be able to organise himself."
All I could say was, "He can't. And the IEP makes that clear. That's all there is to it. Penalising him for not being able to organise himself is like punishing a blind kid for not taking notes down accurately from the blackboard."
Before you can do anything, you need a formal assessment and diagnosis. This makes it possible for the school (with you as the guiding light) to put more appropriate supports in place for him.
You're not going to be able to change much of what he says and does, at least for now. A lot of it - let it ride, for now. Work out what is vital, and only deal with that for now. Where he CAN take control of himself, encourage him. That will make it easier for him to let you help him where he still needs it. He needs to feel loved, safe, supported and relaxed. He's probably feeling none of those things, especially if you're feeling so thoroughly at the end of your rope. I'm not criticising you - you're trying to do the impossible - only pointing out that your stress will be making him worse, which is making you worse, and so on. Something is going to give if you can't find a stop to the cycle. It's not your fault - these kids are much more difficult to parent because we have to throw out the rule book and find new rules as we go.
Good luck, keep us posted on how you're going.
And remember, only with your back to the wall, can you go forward (weak attempt at humour).
Marg