> The slightest thing that doesn't go according to plan will result in a hyper-ventillating breakdown.

They're slight to you, because you have a more developed world-model. They're not slight to him, because they are the foundations of his reality. Talking about different things that can happen, different ways things can be, and their consequences, ahead of time – and then reinforcing that shortly before the change happens (W, so we're going to do X, so Y and Z will happen) – can make it easier to deal with. I'm not sure how much that'll go in, because he's only 4, but this can work with older children.

If these are his own plans going wrong and causing him distress, maybe it's worth teaching him how to plan for contingencies. That includes considering all likely possibilities (i.e., if A then X; if B then Y; if C then Z), and "I plan to make a new plan" for less likely events.

Techniques for managing anxiety might help as well. The general idea is to give him lots of tools with which to process the things he can't currently process. (One model is that autism is a lack of hard-wired, instinctive brain functions that allistic people have. This model is wrong, but sometimes useful.)

> He has poor gross and micro motor skills.

Sounds like dyspraxia, which usually means you have to break actions down into simpler actions and practice those simple actions a lot: sort of like learning a musical instrument. but for everything. Playing with blocks, arts and crafts, and lots of playing outside (somewhere where falling over is safe) can help reduce day-to-day clumsiness, but that will probably always be a difficulty. (I don't know much about dyspraxia.)

> He has an obsessive need for answers and will not accept "we don't know".

Are you sure he's not just playing a call-and-response game? (Does he get upset when you respond "we don't know", or is he just insistently asking questions?)

But yeah… gonna have to side with him on this one. You, as his parents, are his main gateway to the wider world, which is full of lots of really really really interesting things. "We don't know" just shuts down any possible line of inquiry. It's not actionable, even in theory. But knowledge doesn't come from parents: it comes from books, and experience, and science, and study, and we can (almost) always find out things that we don't know yet.

That doesn't necessarily mean you have time to find out the answers to his questions, right when he's asking them.[7] If you can explain that it takes time to find things out, you could make him a list for things he wants to know, and every time he asks something you don't know, you can get him to add it to the list, and then you can go through the list in your own time.

Make sure he can see the list, and add to it himself. If a lot of questions are about a certain topic, you could go to the library and find a relevant book.

If you describe some of the actual questions, I can suggest a more specific approach should you want it. (Some questions, like "how does gravity work", are best resolved by explaining how to do a physics experiment, or perhaps by telling the story of the Delft tower experiment, rather than by trying to explain Newton's laws and the inverse square law.)

Thinking of writing makes me think of school: has he started that yet? If he's going to go to school soon, and he has trouble with change, it might be worth making sure he's got a firm grasp on everything involved ahead of time, possibly including a visit to the school he's going to, so he knows what to expect. (You may be able to take advantage of moving up day.) But, again, he's 4: he might not remember a visit by the time school actually starts.

> This actually causes problems because he cannot help interrupting and cannot wait.

That just sounds like a 4-year-old to me: they're not known for their impulse control. Don't think it's autism-specific. Patiently explaining that it's rude to interrupt, and he should (e.g.) put up his hand and wait if he wants to say something while other people are talking, should get through after the thousandth time or so. (Make sure the thing to do is consistent: putting your hand up makes sense if it's the same as you do in local schools, since there'll be less re-learning and context-switching.)

> there are more behaviours we're concerned about

I can't promise I've seen it before, but your kid sounds fairly typical, so I might be able to give suggestions for those as well, if you like. Do check the websites I've linked first, though: relying on one source is a terrible idea, no matter how much I may think I know everything.

[0]: https://www.autism.org.uk/advice-and-guidance/topics/behavio...

[1]: https://www.autism.org.uk/advice-and-guidance/topics/behavio...

[2]: https://embrace-autism.com/alexithymia-and-autism-guide/

[3]: https://archive.org/details/focusing00gend

[4]: https://www.autismhelpuk.org.uk/post/how-do-you-teach-an-aut...

[5]: https://embrace-autism.com/autistic-verbal-and-nonverbal-com...

[6]: https://autisticnotweird.com/the-stop-rule/

[7]: https://www.smbc-comics.com/comic/why-is-the-sky-blue

[8]: https://mediabiasfactcheck.com/autism-speaks/

[9]: https://www.themarysue.com/the-autism-speaks-controversy-exp...

[10]: https://www.wikihow.com/Boycott-Autism-Speaks