It sounds as though you should have enough evidence to get an application in for a parent request EHCP assessment.
As part of the assessment you can request all sorts of reports from specialists and then the world starts to open up. You can also request to talk to these specialists as part of the process and they can help to address your concerns.
Diagnosis fear is massive. I remember it all to well. The thing is it doesn't get tatooed on your (or your DS's) head.
There are a few circumstances as an adult where it could effect life choices. You have to disclose for a frontline military role - so military service may be out.
There are very few ocassions when it has to be shared. Its his diagnosis for you to use to his advantage. In the most part the only people entitled to what is confidential medical information are those you share it with.
After a few wobbles about labeling, this parenting lark isn't easy, we went with the diagnosis route.
In yr 5 my DS got into an Autism provision. At the time school provision was managing him not doing activities PE, music lessons etc having lots of quiet time and he was not really mark making whilst I knew he was intelligent. All his peers got ahead of him.
With the right schooling, he went from off the bottom of age expected scores to above average SATS in less than 2 years.
We were also able to get Disability Living Allowance, we used this for buying him tech, lots of noise cancelling headphones and ear defenders, plus things like getting a bigger rental on holiday so he could have allocated quiet space. Its given us a better resemlance of family life plus a diagnosis has ment we can be fast tracked through security at airports and seated on planes first - opening up the world.
Moving forwards another smaller battle got us to an Autism provision associated with a mainstream secondary and not without the odd challenge on route we're now expecting some 9's on results day - he got quite a few in his mocks.
DS has just signed a contract for an apprenticeship with a large multinational, not as a special needs nod, but because he's an amazing young man and his varied education has allowed him to become that. I'm degree educated, Mechanical Engineering, but I couldn't of nurtured him in the way he has been at secondary. Its better than a living wage - a proper job within society. Something I could barely have dreamed of back in primary school.
His diagnosis, provision support and EHCP mean we have been able to get assistance with things like transport to school - so I can manage his younger siblings. We/ He is now in receipt of Personal Independance Payments and as EHCP's carry on through to 25 he is getting transitional support into the workplace. For us diagnosis opened many doors. I haven't yet hit any that its closed.