RBBMummy, have you read up on the EYFS Framework? That would give you a pretty good idea what most children can do by the end of reception. But I assume you haven't, as you haven't responded to any suggestions in this regard.
In my DS' reception class, there was one child who could read roughly orange level books upon starting, another who was reading yellow level books. (You can look at e.g. Oxford Reading Owl for free sample books at those levels if you want to find out what that means.) Of the other 28 children, most had had some exposure to letters, might recognise some or all of them, were able to recognise their own names (but not write them), and a few - maybe 5 - were able to blend single CVC words.
At the end of reception, most children were reading yellow level books, with a range from Turquoise to Pink. Some children had still not cracked blending. With regards to phonics, most children knew the main spelling for the 44 sounds, but no alternative spellings nor had they been taught that some letters sometimes make other sounds.
It was in Y2 that the first children started on Harry Potter books.
Regarding maths, the variation upon entry was even bigger, I'd say, as a number of children could not yet count to 10 nor recognise any numbers, whereas two could count beyond 100, add and subtract mentally, knew their 'number bonds', had firm understanding of place value, and were beginning with multiplication (could count in 2s, 10s, 5s). The vast majority however could count to somewhere between 10 and 20 and could perhaps say what is 'one more' than a number in that range.
By the end of reception, they could all count to 20, and most to 100; most could say what is 'one more' or 'one less' than a number within 0-20 and quite a few could do simple addition within 20, with the help of e.g. a number line; they could recognise basic 2d and 3d shapes, and tell o'clock time; some could tell half-past time as well. They had started to learn skip counting (counting in 2s).
Those couple of children who could do all that when they started, weren't really taught anything further during reception year, but had plenty of opportunity to deepen their understanding of mathematical concepts during free play, if they chose to.
I wrote this out in the hope that it will help you get a further idea of what most other children will be able to do upon starting reception, and what they will be learning - in terms of maths and reading - during that first year. I hope you will be able to prepare your DS and scale down his expectations regarding the other children.
Even for NT children, it can be really hard to understand that something that just seems 'obvious' to yourself is not understood by everyone. I can imagine that this might be extra hard for your DS, so good on you for wanting to find out the reality of what most children that age can do, and then manage your DS's expectations.
However this won't tell you anything about how the school will deal with your DS's abilities, or with his difficulties. That, only your school will be able to help you with. So if you want to prepare your DS with regards to what HE will be taught and how learning will be structured for HIM - arrange a meeting with the school as soon as place allocations are definite (16th April for most, unless your place was allocated via the SEN/statement route). Speak to the SENCO and class teacher. I can image they'll suggest to 'wait and see' how it goes when he starts school (with regards to how they will deal with his abilities - they will want to see for themselves what he can do), but you can try to impress on them how much easier things are likely to be if your DS knows what to expect, so any indication as to what they might be doing, at least in the beginning, would be very helpful.