Pilgrim
Just a couple comments for now.
Concerning Numbers 21:8, I think I agree with you here, I don't think the passage is rhetorical. Unless I have missed something in the context of the verse, in order for it to be rhetorical it would at least give a clue that it is rhetorical. I don't see one.
Concerning "whosoever believeth in him" and the Greek. This is an area that I know very little about.
I must admit that "Whosoever believeth in Him" compared for example.
Young's Literal Translation (YLT)
16for God did so love the world, that His Son -- the only begotten -- He gave, that every one who is believing in him may not perish, but may have life age-during.
I really do not see a lot of difference either way.
I would agree that there is a difference if I accepted the Arminian understanding. However, as a Calvinist all "Whosover believeth in Him" tells me is that in order to have life one must believe in Him.
How is this different than other translations? (Why do I get the feeling I am missing something?)

I will say that I don't see anything rhetorical, for the fact is only the elect believe.
If I remember correctly the A.V. was translated from a different translation of the Greek (Textus Receptus?). I would be interested in seeing the literal English translation is from that text and how it compares to the A.V. rendering.
Although I would agree that knowing a little Greek isn't enough and I would also agree with one must add to that knowledge. That is where my agreement with the author ends.
Where in the context of the passage and the greater whole of Scripture does the author see that a "rhetorical stategy" in the verse?
Sorry, no time to say more, or for that matter check for spelling/gramer mistakes. I need to go to bed.
Tom