1. To those who accept the evidence that it is, yes.
2. To those who accept the evidence that it is, yes.
3. To those who accept the evidence that it is, yes.
4. To what end?
5. Um, I think you're going too far here. What do you mean by "incontrovertible," exactly? What sort of truth are you talking about? All truth? Spiritual truth? Would you say 1+1=2 is incontrovertibly true? I would. Does this mean, to your way of thinking, that a mathematics textbook would also be "incontrovertible"?
Hmmm...I certainly hold to the idea of Sola Scriptura but I think "There is only Sola Scriptura" is a bit over-the-top.
Did the Early Church establish the truth of Scripture? Did it confer spiritual authority upon the canon of Scripture? I don't think so. The Early Church (not the RC church) merely recognized the truth and divine origin of Scripture and adopted those texts so recognized as the word of God. The Early Church, however, did not make Scripture true and/or divinely inspired. Those texts constituting the canon of Scripture were authoritative and God-breathed long before the RC Church formally acknowledged that they were.
Selah.