In my fourth year of my PhD on schizophrenia and I'm currently writing up my thesis. I'm procrastinating right now so thought I'd do something useful with what I've been studying.
And no, schizophrenia is not multiple personality disorder.
Edit: I have to get dinner and run some errands. I'm really enjoying this so I will definitely get back and answer the rest of the questions.
You're correct in that visual hallucinations are much rarer than auditory hallucinations (although they do exist).
I'm not familiar with how genetics work wrt/ autism. There is a genetic link with schizophrenia (if a relative has it, you're more likely to have it as well) but it is not really clear what the interaction is. For example, Huntington's Disease is caused by a single defective gene. As far as we know, there is no "schizophrenia gene".
I've never encountered deaf schizophrenic people in my research, so I just did a quick Google search and found this:
https://www.ucl.ac.uk/news/2007/jul/exploring-how-deaf-people-hear-voice-hallucinations
This is melting my brain, thank you!