. . . the sufficiency of Scripture is an absolutely essential doctrine for a Christian.

I've known hundreds of Christians over the years, and had theological discussions with many of them. Since you are only the fourth person I've ever "talked" to who thinks this, what do you call the other 99.99% who call themselves Christians?

"God exists because the Bible says so and the Bible is correct because it's the word of God" is circular reasoning. The premise and the conclusion depend on each other, leading you in a logical circle. The conclusion never comes out -- round and round it goes, chasing it's tail.

"Everything the Bible says is true" is fallacious reasoning, in that it is both unproven and unprovable. Your interpretations of the Bible are fallacious in that the Bible is extremely self-contradictory, and there is no way to reconcile it to itself if you are going to take it literally. The message of Christ and the God of the Old Testament do not mix, and yet you say that it is all literally true and should be a guide for how to live our lives. Failure to believe in known facts about how our world works is also fallacious reasoning, in that your arguments are based on ignoring huge bodies of knowledge. Your conclusions have nothing to hang their hat on.