Deutero-Isaiah-What do you Think?

In a previous essay, I had spoken about the Documentary Hypothesis, a theory that reflects multiple authorship of the first five books of the Bible (the Pentateuch)  In this essay, I would like to speak about the view that the book of the prophet Isaiah was written by more than one person.  This alleged second author is also referred to as Isaiah because he allegedly wanted to remain faithful to the theology of the first Isaiah.
This supposed author is referred to as Deutero-Isaiah, or Second Isaiah.

There are three basic reasons why some biblical scholars, theologians, and ministers believe that there was more than one hand involved in the composition of the work which bears Isaiah's name.  Those reasons are as follows:

1.  Difference of literary style between chapters 1-39 and the rest of the book.  The style of writing in the first 39 chapters are of a sad and gloomy nature, reflecting despondency and depression.  The writing style of chapters 40 through the rest of the book are more jovial and celebratory.   Interestingly enough, some years ago, I was reading the book of Isaiah in the King James Version.  I was not paying attention to issues of literary style or any of those things that normally come along with the analysis of literary documents.  I was more interested in the theological content of the book.  In spite of that, however, the differences in literary style between the first 39 chapters and the rest of the book imposed themselves on me. I found it amazing that a book which was written in the Hebrew language would reflect the same literary differences in the English language.

2.  The scenes described from chapter 40 on, are scenes that could only be described by a person living in those times.  The 40th and subsequent chapters of Isaiah describe scenes that would have only been familiar to someone living in the time of the Babylonian Exile or afterwards. So those who advocate for the Second Isaiah point of view, tend to believe that First Isaiah lived prior to the Exile and that Second Isaiah lived during or after the Exile.

3.  First Isaiah speaks of a tribal, nationalistic, and provincial god, i.e. the God of Israel.  Second Isaiah speaks a global and universal god, who is concerned with all the nations of humankind.  Second Isaiah's god is more of a cosmic deity, where First Isaiah's god is one who is more restricted to one nation.

Our questions, then, are the following:

1.  At the end of the day, does it make any difference whether there is one Isaiah or multiple Isaiahs?
2.  Is the number of authors named Isaiah relevant to the doctrine of the divine inspiration of the Bible?
3.  Is the issue of how many people named Isaiah relevant to the way we do biblical theology?
4.  Does the issue of whether there was one or two people named Isaiah relevant to how we get "the cheese off the truck" (survive) economically and socially?

Tell us what you think relative to any or all of these questions.  Your input is valuable and will be appreciated.

Grace and peace,

Dr. Juan A. Ayala-Carmona