I am going through similar with my daughter right now. She has not begun the tantrums or hurting me but I know she is EXTREMELY frustrated since she is barely talking! She does know some sign language and that has helped and I try to keep questions to yes and no so she can tell me in words or nodding her head.
Does you son do any signing? I would try to do that or do pictures of things that he may want and he can show you the picture if he can not communicate it. I am sure the speech therapist will help you to come up with a way to do this to benefit him.
Be patient with him, he is definately going through a lot all at once! I believe some of the behaviours may be just ways of getting even more attention from you, even if it is negative attention! Of course at the same time, do not allow him to get away with them!
I have not done time out with my daughter because I know she does not understand the concept of it and she can not communicate the whys of her behaviours so I feel I can not do this because she may have what she believes is a legit reason behind some things. We do sit down and I explain what is wrong and give a little extra loving- most of the time this stops it right in its tracks. She will then show me what she needs by signing it or bringing me to where she wants. Of course I will admit there has been times for everyones sake I have put her in her crib and let her cry while I go in another room and do the same! lol
I can only imagine how frustrating it has all got to be for you! I could not do what you do- and to have 2 in diapers at once! OH MY!
Good luck with everything and many blessings to you and your family!