Apply for the ehcp. The threshold for an assessment is very low and from your first post it can be argued that he meets the assessment threshold and therefore any needs and the provision to meet them cannot be fully known without a full assessment.
Have a look at ipsea and sossen websites. They have telephone consultations for support. Ipsea you normally have to book but they used to have one on a Friday morning that you could just call in on. Sossen have times for call ins listed on their website they also have in person drop ins depending where you are in the UK. Stay clear of sendiass, they aren't always independent of the LA and therefore any advice is subject to this bias.
The fact that you are seeing an OT who has suggested an EHCP is good evidence.
Being academic is not a legal reason for an ehcp to be put in place or an assessment to be made.
Emotional support/ regulation is listed in the areas of need in the sen code of practice. OT intervention is detailed as being a health need do vital to education that it is a sen and should be detailed in an ehcp as such (wrote in section B with provision in section f specific and quantified) there is case law around this too. Safety is clearly an issue too and likely understanding social concepts.
Apply as soon as you can, he is seven years old and it may take a while to get things in place.
As part of the application state that you would like:-
speech and language assessment (social needs? Understanding language, inference, not taking things literally, theory of mind, setting up ways he can communicate things, training the teacher and possible/ highly likely ta). Have a look at the report from when he was diagnosed as this will give an indication of areas that will likely need further exploration.
OT I'm guessing you'll need a sensory assessment. Speak to your current OT and see what she recommends. Ask for her to put anything he 'needs' as setting he needs rather than recommendations including how often, by who, if any physical adjustments or equipment are required, how often he needs to be seen for how long, who will need training, who will review anything put into place. An ehcp would fund this if you are currently paying out of pocket. Does he have dyspraxia or hypermobility? What provision do these require? Do they need formally diagnosing?
Educational Psychologist, he's getting frustrated that some work isn't suitable and working at a higher level in maths. You could do with him being assessed to see what his understanding is if the work isn't straight forward or if it starts to be presented differently.
Make sure any assessments are based on recognised assessments and not just observations. All needs documented, provision to meet the detailed, quantified and specified.
Any provision shouldn't be wrote in a way that allows it to be changed without going through annual review or by saying things like x will be assessed in the future. If the nhs or other organisations the LA commission have long waiting lists they should be paying for an independent to do the assessment.
Have a think if you want a social care assessment for things like short breaks. You can ask for one at assessment as well.
You have the right to request any assessment that he reasonably needs. Are there any other areas?
You may have to go to tribunal either to get the assessment or to get the plan wrote in a legally conforming way. Don't let this stop you. Most tribunals (I think around 90/95% are won by parents znd carers). Many times you won't even get to a hearing. It's just the LA wasting time, as the longer provision isn't in place the cheaper it is for them.
Don't be afraid to make the LA keep to deadlines or to enforce any of your rights.
There are many myths around ehcps. teachers, sendco's and the LA can be guilty of perpetuating them. Many parents don't know their rights either, sometimes parent carer forums aren't the best place for info especially In regards to this.
Join Educational equality on Facebook. There is lots of great advice there.
Apply yourself, as soon as possible.