I would write what I said. Yes, you can write what Payrol guy says, but the hearing is free for the asking. The employer gets a copy. Saying "wrong" makes you sound just nutty enough that the many employers will think, "this guy doesn't stand a chance with an appeal written like that," and be further incented to skip the hearing.
Being "wrong" is a reason. People waste HOURS writing these things. Don't do that. The real magic happens at the hearing with testimony and evidence. Nothing you write will win you a hearing.
You could write, "I APPEAL!!!!" in crayon on a grocery bag. This first-level appeal is free for the asking.
No. Testimony is evidence, you reading from a piece of paper, not so much. The employer will be talking first if they even show up. There is no way what you write will make sense with you not knowing what the employer is going to say.
You can have them with you, but while waiting for hopefully in-person hearing, when you see that the employer isn't coming, do NOT submit them. I don't think they are relevant. The way I read your story, the CEO fired you. He needs to provide the reason and proof, and any failure that the author of your text message gave isn't first-hand, and is hearsay.

