I am so sorry vickibee.
I found my husband dead in April, we had separated but were still close. My eldest child also has ASD, sounds similar to your boy although younger, mine is 10. My children have had counselling organised by the school, they have had 4 out of 6 sessions now, they started just after half-term. Both kids have really enjoyed the sessions. One thing the counsellor said was that we all grieve differently, and just because my son does it his way that's not necessarily wrong. I was worried that he didn't want to talk about how he was feeling although we do talk about their dad generally all the time. The other thing we do is always say goodnight to Dad and tell him something about the day. (We talk about the fact we come from the stars and go back to the stars, so we talk to Dad up in the stars, this seems to work for mine.)
Just be led by what he wants to do for now. Mine both wanted to go back to school on the 2nd day after and my son has largely been in pretty much all the time. My daughter who is 7 has wanted to stay at home a bit more but generally again has found being in school really helpful.
I also spoke to the head teacher with the kids about telling their classmates and they both agreed they wanted their class teacher to tell the class straight away whilst they were in the classroom but without them having to say anything. Again, your son is older but it might be worth asking him what he wants to do here.
Winstons Wish that has been mentioned had some info on grief and SEN that was helpful to read. They also talked through things that might be useful to help the children. I also got memory boxes from them for the children.
You will be in such a massive shock for now. I couldn't eat for the first 24 hours but had hot chocolate then smoothies and porridge, just simple things.
I second the recommendation for "It's ok that you're not ok" book. I also found Resilient Grieving by Lucy Hone brilliant. But to start with I couldn't really concentrate on a book. I had one page a day book that helped: MArtha Hickman "Healing after loss" as I only had to read a few words a day. A good book for your son (and you) might be "Tear Soup". The other books my children have are probably aimed at younger children.
Given your son's age, it might be helpful for him to contribute to the eulogy. I found it helpful for me to write it. I also read it to the children before the funeral so they were prepared for what it said and knew what to expect (which is important for my son).
Given the sudden nature of my husband's death there was a coroner involved and it took some time so the funeral was actually 3 weeks after he died. It felt like an inordinate amount of time waiting for both the coroner (think it took nearly 2 weeks to get an answer) and the funeral but they said it does just take a while nowadays.
You probably won't be able to absorb all this information now but everyone's messages will be here to come back to. Feel free to PM me. I'll add more if I think of anything.