With the ehcp, it does sound like he meets the assessment criteria. Section F of the ehcp is the provision and section b his needs. It should work needs- provision- outcomes but very often doesn't.
You need evidence from professionals or documents such as meeting minutes for detailing his needs. Parent representations aren't often used forshowing need unfortunately l(they are sometimes I know). The charity Sheep mentioned is worth a shout.
The provisions required to meet the needs should come from professional reports. These should be specified, quantified and detailed so to leave no doubt as to what must be provided eg a level 3 ta trained in x to provide 1:1 support during all lesson time. Class sizes no greater than five children. If the reports aren't detailed like this you can ask the la to go back to the writer for this detail. In reality most parents end up paying for private reports to get this level of detail.
Ot is occupational therapy. They help massively with many things including sensory needs, motor skills and emotional regulation.
When you eventually get the la to agree to an ehcpa you are allowed to request that your ds is assessed by a professional if it is reasonable (he likely has needs in ti's area). From what you've wrote I would want as a minimum an educational Psychologist, speech therapy and occupational therapy reports and think it would be reasonable for you to request them.
The LA has a statutory duty to assess for all sen within the ehcp assessment timeframe. If there are waiting lists they should pay for private reports. They should get the asd assessment completed as part of this (if it hasn't already been done) as they cannot possibly meet their statutory requirements if they don't.
It's highly unlikely that te primary school only have one document. Do the sar again and use a template asking for all info including notes, emails, documents, attendance details, referals, communication with other agencies etc.
The la may just turn down your parental request anyway as a delay tactic (it saves them money). I'm not sure if im allowed to mention Facebook groups that may help so I'll put a couple in a separate post incase it needs deleting (sorry mumsnet if that's the case).
Both ipsea and sossen have helplines, please use them for help/support. Sossen sell some little books which are amazingly good, I think they are about £5. The tribunal one is very good ad well worth the money. (It's a charity, I don't work for them so not out to make money).
It's a battle for most families so knowledge is power.
Sendiass services in some areas can be quite good but many are funded by the la and tow their line/ local policy which isn't always the lawful policy.
The sen code of practice and the noddy guide are fantastic (they're worth knowing about for the future).