Congratulations Emily on your appointment. Your question is not so simple to respond in a post. For example, there is a distinction to be made between SEN / D. In theory the SEN register (K data) are those in receipt of ‘additionality’ at the time of recording. So it is possible to have a child as SEN, but is making progress through HQT and therefore technically would not be on the register, but a monitoring list. Interventions also need to classified into short terms and long term. Disability is about reasonable adjustments.
Sounds as if you are inheriting a system, that has no framework. I am attaching a New to SENCO accredited course TeamADL deliver that helps with the leadership and management of the fundamental stuff. The course is about enabling you to create a framework to lead. To book click here https://forms.gle/CqsEmYdtgTGfK1PF9