Hi,
Yes, he needs a chewy tube I think. My son wears one, absolutely needs it or he chews his clothes to pieces. Try and work out if he likes to chew soft or hard things, bumpy or smooth so you know which types he will probably like. You can attach it to a cord around his neck if it doesn't come on one. Make sure it has a quick release clasp on the cord/lanyard if you do this so he won't strangle himself. He will still want to chew/ lick other things until he gets used to that though so just keep redirecting him back to it, using the same language each time. Much more hygenic, for him and others, than chewing random things.
For the "first then...' you can try to keep the first thing very brief... have the card with the 2 activities. Make the first quick, lots of positive language when it's finished... even if he is upset and then quickly on to the next. He will learn the "first then..." schedule... but doesn't mean he will always like it!
my son at 13 still gets upset if he has to do something first he doesn't want to.... but he does it, which he didn't used to. Try to make the second thing a thing he loves in the beginning. Eg. he won't really want to listen if you tell him "story then music time" if he hates both. As he gets better you add more steps and as he gets more able to handle it you can add more undesirable things as long as he gets his fun things too. Also we used a "finished" box or pocket, where he puts the card that represents the activity that has been completed. A visual for that ending and time to move on, especially helpful when it is time to finish a preferred activity. The finished symbol that was a black and white checked pattern, like the finished flag in a car race. You can carry some of these cards on a keyring with you, learn the signs to go with them, and use the cards at the same time you use the signs and speak the words. When my son was starting, we had "finished", "wait", "toilet", "help", that was it. If he wanted help, we would show the card, do the sign, say "help" then the words "you need help" or "I can help" and then assist. He may not seem to be looking, don't assume he isn't though. My son, and I've heard this from others too, has great peripheral vision. He can see those pics without looking directly at them, he can also see me sneaking the biscuit container out of the pantry when he appears to be not looking!
You sound like you have a really great starting knowledge, and you already have a connection with him which is great and you want to help... he sounds like a lucky boy. Keep pushing him gently and he hopefully will reach out even more.
I agree with the others, to push for help from outside... I don't know where you are but he should surely be eligible for help from O/T, speech at the very least. If I think of anything else that helped in our situation, or I saw helped others, I 'll post again. Good luck!