How do I get an EHCP without a diagnosis and how do I access an alternate provision if we don't get an EHCP?

I have a 13 yr old son who has been home educated since Sep 25. We were failed by our primary school when they kept referring him for ASD and ADHD and telling us that he was "managing with scaffolding" when he was clearly struggling and failed all his SATs. He went to a private school for 1 year and they deferred him back a year because of his delayed learning, they did a Sandwell assessment that showed he was working at 7-8years old in every area, but then the school closed down so we chose to home educate (there was huge anxiety around school and learning and it had started manifesting as self harm also).

Since doing so we have realised just how far behind he is. The only official diagnosis we have is a visual processing disorder and after 3 ASD and ADHD referrals they all came back as inconclusive. We have an anxiety related Tourettes diagnosis and the consultant there wrote that he has an obvious learning disorder but then discharged us so we have no follow up for that. Our GP has just told us to get in touch with the LA to get an EHCP but I dont think that will do much good when hes home ed so we have no capacity for an ed-psych or similar. We are struggling with traditional home-ed as there is severe anxiety around learning in the traditional sense so I would like to let him access an alternative provision for 1 or 2 days a week but I cant even find anything that we can fund privately.

So I suppose my question is in 3 parts -
1. do I need to get a diagnosis or where do I get any support for a "learning disorder" and how do we find out the full extent of it? (hes had testing for global delay that was negative)
2. I know I need to start the process for an EHCP but Im at a loss how I do this as a home educator and without a diagnosis and no professional/medical support?
3. Is an EHCP the only way to access an alternative provision?