3. If God was so inclined to "physically" write the Ten Commandments in stone tablets "himself", then why would he decide to write the remainder of the Bible through the hands of so many men over such a long period? Indeed, if he was willing to write one part, then why not write it all so that there would be no question of "his word" being preserved?

As it is, it seems there are redundancies and even contradictions in the human writings (for example, the Gospels, where the same story of Jesus is retold, but with differences in style, content, and even descriptions of the same events) which would not be present if God had simply composed the entire Bible himself.

Your question of why God did not chose to write the entire Bible, since he apparently physically composed the ten commandments is an interesting one. It is loosely analogous to the question that arrises when someone wonders why God would sometimes use angels to bring a message to someone, and sometimes come directly, or at other times use human intermediaries. Or why did God choose to talk to a certain person, rather than another, or why did Jesus heal these folks and not those -- or for that matter, why did God pick Abraham and his descendants to work through and not some other person and his (or her!) descendants. Frankly, there is no good answer to any of these questions, other than to say simply that God, being God, will pretty much do whatever he darn well feels like doing. Sort of like the story of the five hundred pound gorrilla and his sleeping arrangements.

This is obviously not an entirely satisfactory answer, but I've found that the Bible rarely offers us answers to "why" questions of this sort. It may be useful to point out that the ten commandments are the only portion of scripture for which it is claimed that God physically wrote them down, so the human instrument method seems to be normative. Of course, one must point out that the appearance in the Bible of even the ten commandments is then the result of the author of Exodus copying them from the tablets to the scrolls he was using for the rest of God's words.

In regard to the differences of style, content, and descriptions of events in the Gospels (or in other parallel accounts, say comparing 1-2 Samuel, 1-2 Kings and 1-2 Chronicles), such variations clearly indicate that they are the products of several human beings doing the writing, each with his or her own perspective and methods of expression. We would assume that this sort of variation was something that God wanted.

The presence of contradictions, however, may simply be the result of our limited data and understanding, not necessarily because they accounts genuinely contradict. The authors were not intending to give us history or a complete accounting of events, and so they were very selective in what they presented (notice what the author of the Gospel of John writes at the end of his work in John 21:25).

One also has to take into account the differences in narrative structure between the way the ancient Jewish people wrote and the way we as westerners (following Greek and Roman narrative techniques) would compose matterials. (For more information on this aspect of your question, you might like to read the article in the Quartz Hill Journal of Theology, The Thematic Arrangement of Biblical Texts).