HELP! EHCP Annual Review

Hi,

My son has been diagnosed with ASD. He is in Year 2 and attends the ASD Base. In a week's time he will have an annual review of his EHCP. I contacted the school and asked for any documentation before the meeting and the school said that they will let the therapists know that I made a request for reports. I thought that it is the school's responsibility to provide parents with all the reports and other documents. In the past, I asked for some written views from the teachers but the headteacher said that I can ask them for their opinions straight at the school gate and obviously this was not what I wanted. I would like to prepare myself for the meeting and want to know in advance what the teachers/therapists think about my son's development. Moreover, I have got a feeling that an OT therapist does not support my son enough. She is often out of work and we have never received any outcomes, any progress/evidence log from her. During the lockdown we had only one online session. How could I challenge it? My son has serious sensory integration difficulties and he needs constant OT support. The school receives funds from the Local Authority for the therapies so where does the money go? My son was given 6 sessions of 45 minutes per term and I expected the school to provide my son with the provision he deserved (the provision he got with his care plan actually). Would it be possible to apply for a personal budget in order to pay for his private OT treatment? 
Another thing is about the amendments that I want to make in my son's EHCP. The headteacher said that this plan does not have to be changed every year only when a transition takes place so what is the point of arranging annual reviews. My son's EHCP contains information that is not relevant. Many paragraphs in sections B and F need to be updated and also there is missing information about an OT therapist involvement in my son's learning process. What do you think about it? Am I panicking too much? 
I would be grateful for your comments.
Many thanks!