I agree.
There is no “Authority to authoritatively establish the Word of God in writing.”
I think I agree with your intent, but the exact wording here I have issue wit — of course there is authority given to establish God's word in writing; we see this explicitly in Revelation where John is told to write unto the seven churches which are in Asia
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The ancient scriptures were assembled based on the proven truthfulness of the prophets, long after those prophets had been murdered for obeying Yehova.
True.
Only those that were handed down in Hebrew are “scripture.”
Not strictly true; largish portions [chapters] of Daniel and Ezra were in Aramaic.
These scriptures were affirmed by Yeshua himself. Nothing written after his death has such assurance, and the selection thereof is arbitrary, and has changed from time to time.
Again citing Revelation above, I'd hesitate to make this claim.
Daniel 4 was in aramaic, because it is the personal testimony of Nebuchadnezzar, not the writings of Daniel.
A few aramaic words in other books because they have no parallel in Hebrew.