You haven't mentioned section i (placement) are you not appealing this too?
Check to see if you qualify for legal aid.
Sossen are also very good. They have an ehcp check service (I can't remember the cost bit it isn't £100's) these are great for grounds of appeal and pointing out where the ehcp is lacking.
All special educational needs must be detailed in section B. Go through all reports and documents snd make sure this is the case and make sure that they aren't detailed as 'strengths' when they are a need.
Are there any indications in your reports that other needs require assessing? Eg something saying that your son has sensory needs but no sensory assessment has taken place?
Are the assessments that have been completed and used standardised so that progress can be measured? Make sure the professionals haven't just cited their opinion without evidence to back it up. (If you want to challenge).
Every need in section B must have provision detailed to meet it in Section F. The provision must be specified, quantified and detailed so that it is clear what must be provided.
Do you have a placement in mind? If so, do they think they can meet his needs? Find something thatthey offer that your son requires that the school the LA have named cannot provide.
Sossen also have some great little booklets that are about £6. The appeal one is fantastic and more than worth it.
If you start looking at the working document make sure you follow the key as per the court docs. Make sure you meet every deadline bit be prepared for the LA not to.
When you get the bundle double check everything is there.
You may need inde reports or additional evidence.