The reason it is a good idea to get an EHCP before secondary is that those with an EHCP who name a school on the plan must be accepted by that school.
This means if you find a mainstream school , that you believe would better suit your child than the local one they would normally attend, they have to accept you. This is not the same if you are choosing a special school but it does apply for mainstream ones.
Think of the EHCP as an opportunity for you to choose the best mainstream school for your child regardless of catchment, rather than a way of ensuring a (possibly unwilling) school provides support
Find a school that is near enough to go to that will provide the best support and use the EHCP to make sure you can get in there, in case it is not your local catchment school
Oftenbest SEN support is given by schools that are not 'outstanding'. Most outstanding schools are like that because they have a high exclusion rate
You need a good school with good results but low exclusion rates and a convincing SENCO and SEN policy. Schools get good at dealing with SEN by - dealing with enough if it.
You may have to fund transport if the school you want is far away but the school can't turn down your application.
Looked after children and children with EHCPs have top priority in school applications