There's an autism advisory clinic? 
What is that? What do they do? Who staffs it? You should I expect at least find out first what they are for.
I would advise you to find specific problems that needs solutions, rather than getting referrals all over the shop for generic 'help'.
That way, the help you receive is for that which YOU have defined as needing rather than help someone else has said you need because it fits in with what they like delivering iyswim.
So, your ds has HFA. How old is he, and does he go to school?
If so, at school does he get any support? If so, do you know what for, and for how long, or anything about the strategies they are using and their relevance for your ds? Are these strategies working? If so, how do they know? Does he have an IEP or any targets
These are probably the things you should discuss with the SENCO in the first instance and once you have, follow up the discussion with a 'thank you email and confirmation of everything she has said'.
Then you need to satisfy yourself that she is meeting your child's needs. I imagine probably not, if you are thinking of applying for a SA, but if on the otherhand the school really are meeting his needs then you will not get a statement.
The journey towards a statement is a rough one. It will involve without doubt, the involvement of the Autism Advisory Service which is one very good reason not to apply unless absolutely necessary invho.