I have a son that was diagnosed with Apraxia at the age of 2. IT IS NOT normal for a child not to be talking about that age, they are not LATE TALKERS, they just might have a speech delay. I would highly suggest you get a complete speech evaluation from a certified Speech Language Pathologist. Unfortunately, I don't know anything about the center that you mentioned, my son has received private speech therapy from an SLP at All Children's Hospital Specialty Center.
Disiplining him, just because your son can not communicate with you does not mean that he can not hear you or understand you. With hitting, when my son hit one of his brothers, I immediately put him in time out and explained to him that I understand that he is upset or mad, but hitting is not allowed and because of his behavior, he must sit in time out for 2 minutes (one minute for every age). When his time out is up, say to him again, you understand that he is upset or mad, but he needs to come to you and TRY to tell you what is wrong. Even if it is "jargon", it is showing him that he can talk to you.
Communicating with him, sign language is wonderful way of communicating, however, your therapist is right. If you rely too much on signing and not speaking, your son will not try to speak to you but use signs instead and that is not what you want. I would also suggest using pictures. Put pictures on your refrige, like juice, milk, whatever... and when he wants something, you talk him to the board and have him point out what he wants and then repeat the word with him three times (our therapist had use do this!). Something else, I know this sounds funny, but when making the pictures, try to use realistics type pictures, not cartoons, we don't live in a cartoon world, it would be easier for him to put things together when they look like the real thing.
Potty training, having three boys now under the age of 4, I didn't start potty training them until they were three years old. But when that time comes, use the picture board.
Pacifier, I would hold off on getting rid of that right now, especially since he only uses it during bedtime. He is going to be going through a lot of big changes in his life in the next few months and he needs that security.
If you have any questions about Apraxia, please let me know!
Good luck!
Remember, one day at a time, one word at a time!