Frog
In a very similar position, minus the ASD.
My suggestion, from experience, is that clothes and makeup - anything that comes under the heading 'presentation' is totally fine. I don't give a toss if my feminine son wears a dress and nail polish. Rock on.
Carefully assess if child is being exposed to homophobia at school or at home. Feminine boys need to know that it's Ok to be gay (if they are).
Look for professional health care from a psychologist or psychiatrist outside the gender clinics. This is so your child can be assessed, treated and supported for any co-morbid mental health issues or trauma going on. Your child may or may not be given a diagnosis of gender dysphoria.
If your child is diagnosed, and has significant distress attached to that diagnosis, seek out DBT therapy for them if you can. This is especially important if they have any suicidal ideation. DBT is an effective treatment for suicidality.
Delay any medical (definitely surgical) treatments as you can. This is because developmentally, teens are in a process of identity formation. You don't want to foreclose on their identity prematurely. Let them get to adulthood with as many options, including transition, still open to them as possible.
Some watchful waiting families are prepared to use female names and female pronouns for their male child; we don't do that in our home, as we dont feel it is in our child's best long term interests. I have been clear with ds that transition (social, medical, surgical) is a huge decision, and one best made with a healthy, adult, cognitively developed mind.
Personally, I do not endorse ds using female facilities. He uses single stall unisex provision by preference. Luckily there is plenty of such provision where we are.
It is entirely possible to support a child who is playing with gender expression, or even a child who has gender dysphoria, without moving too fast.
Good luck with it all.