It's my understanding that ASD and Childhood Onset Schizophrenia are two separate conditions (which can share some features) although a person can have ASD and have comorbid Schizophrenia or other comorbids like Depression or Seizures or Tourette's Syndrome, etc..
Some of your questions I personally don't know the answer. There are lots of medical articles and more online if you want to delve through it all. I think like a lot of things, the researchers are finding out more and more as time goes on.
Some quite commonly used medications can cause some symptoms which can be frightening. I know someone who was taking Inderal (Propranolol), which is a Beta Blocker, for Anxiety and they experienced auditory and visual hallucinations when they first started the med.. My son who has ASD experienced some visual hallucinations when prescribed Risperdal (Risperidone) briefly as a child.
Here's one example...
Autism and Schizophrenia
By Yael Dvir, MD and Jean A. Frazier, MD | March 15, 2011