An hour before curtain. An assistive device is fine. If you need special accomodation contact the theater in advance.
I think you will be fine, especially in your case. I would bring some type of proof just in case they are uptight about it but honestly you should be fine.
At the 8:00 concert I attended, the doors opened at 7:00. IDK about the pillow, but I doubt you will have a problem.
Sorry don't know. I think you can bring a pillow.
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