If you want to get an idea of how the torah changed over time, you should compare the Masoretic text with the Samaritan Torah as well as the Dead Sea Scrolls and the Septuagint. (The Greek translation was made centuries before vowel points were introduced into Hebrew and so may reflect an older tradition of how to interpret the consonant-only text.)
Most of the changes are very minor and have no theological significance. (Differing guesses on how to interpolate the vowels makes a much bigger difference.) Still it is pretty clear that the original would have been somewhere between the Jewish and the Samaritan versions.
I wouldn't say that the Samaritan version is right in insisting that God must be worshiped only at Mount Gerizim, but they are probably right in identifying that location as opposed to Mount Zion as Mount Moriah. Otherwise you have a confusing situation where Abraham almost sacrificed Isaac on a mountain in the remote wilderness that also happened to be in the center of a major city that already existed and was being ruled by Melchizedek.
The Samaritan version is still written using the Paleo-Hebrew abjad (an alphabet without any way of expressing vowels), which the Jews abandoned in favor of a stylized form of Aramaic script a little over 2000 years ago.
It was originally transmitted orally before it was written down. Moses is described as reciting all the Torah for the people to hear, not writing anything more than the ten commandments. This does not however justify orthodox Jewish notions of the oral tradition. The bible is states clearly that the Torah was lost for generations, and that when a copy of the text was found in the temple people were surprised to find what it contained. The oral account would not have survived that period intact.
Far more distortion happens during translation and exegesis than during the transmission and copying of the texts in the original languages. A lot of misunderstandings were introduced by Augustine, who somehow came to be seen as a foremost authority on the bible despite flunking Greek and never even trying to learn Hebrew. He is the one who popularized the doctrine of Eternal Damnation (which was already dogma in his native North Africa, but considered no more valid than conditional immortality or universal reconciliation elsewhere) and insisted that phrases like "unto the ages of the ages" were idioms referring to infinite rather than extremely long finite periods of time.
Gehenna was the Valley of the Sons of Hinnom, which at one point had been a cult site where Canaanites and some Israelites killed their own children by fire in sacrifice to the false god Moloch. In order to prevent this most evil cult from coming back, the site was made into Jerusalem's garbage dumb, where refuse was incinerated day and night. It was also a place to dump bodies of animals and of humans whose sins were so vile that they were considered unworthy of a proper burial. It was not a place of torture, but a place to destroy the last remains of things that no one wanted to think about.
"Hell" literally means "concealed" and is actually a decent translation of Hades, which literally means "the unseen." We tend to think of Hades in terms of Greek myths about where the souls of the dead (especially the wicked) go, but it had broader meanings that that. It could refer to anything hidden below the surface of the earth. The god Hades presided not only over the dead, but also over the extraction of mineral wealth and the burying of seeds in order that they might grow. Descending into hades does not have to have any sort of mystical meaning pertaining to a departed soul. It can refer quite literally to a body being physically buried in the grave.
Sheal literally means "pit," and referred primarily to the grave in which a dead body was buried. Some groups of Jews (particularly Hellenized ones) pictured some sort of afterlife for the shades of the departed, but the book of Ecclesiastes makes it pretty clear that the dead are not conscious.
Traditional definitions of omnipotence have been limited to only those things which are logically possible. Similarly, some prefer to define omniscience as knowing all things that are possible to know, and posit that the future is not yet determined as so impossible to know (although a full knowledge of the past would allow for some pretty accurate predictions, and omnipotence would allow one to make his predictions come true.)
The only part of the bible that actually describes God as omnipotent is probably a poor translation of a term better rendered as "self-sufficient."
