According to Joseph Smith, the reason the plates were given to him in Reformed Egyptian (not a language but a writing system that transcribes Hebrew words into some form of Egyptian script) is that that was what was used by the ancient prophets who wrote the Book of Mormon. Twelve people would later testify that they had seen the plates (3 said an angel showed it to them) and all of them stuck by this testimony even though most split with Smith for other reasons. We believe that said angel (Moroni, son of Mormon) then took the plates back because they would not be safe in anyone else's hands - that was a lot of gold. And as Mattbrown said, there was no compelling reason to fake it - many charlatans made better money in religion without presenting 'scripture', and Joseph Smith did die for it eventually.
There is no LDS doctrine on where in the New World the events of the Book of Mormon are said to have happened. They seem to me to be consistent with Mesoamerica, although on a small scale and 2000 years ago, which would explain why there is no archeological evidence. In addition, according to the Book itself, most of the references to things like iron and horses were made by Moroni, writing several hundred years after they were said to have occured, and he may have been mistaken on some historical details.
There is also no LDS doctrine on ID/evolution - members can believe what they want. As far as I know, Brigham Young University, run by the church, teaches standard evolution (which I find to be closer to the spirit of LDS doctrine than ID anyway, but that's an opinion).
Regarding the Word of Wisdom - we don't drink coffee, tea, et al (actually herbal teas are allowed) not primarily for the health benefits but because we believe God commanded us not to. To be sure, the health benefits we gain by never drinking or smoking outweigh the minor losses from whatever helpful acids tea supposedly gives, but that's a secondary benefit - first of all is obedience. The prohibiton doesn't actually apply to caffiene, only coffee and some teas, but many members feel caffienated beverages violate the spirit if not the letter of the law.
Regarding homosexuality - in the church we believe that God speaks to prophets not just anciently (ie the Bible) but can do so in modern times and clarify points of doctrine. Thus we believe that God does now and has always prohibited any sexual intercourse outside of what He considers marriage (which we believe is only a man and a woman) which prohibits homosexual activities as well. As recently as 1995, the man we believe is a prophet issued a statement that clarifies this. So I have no problems with homosexuals as human beings, and don't even really oppose things like gay marriage, and I realize that the Biblical prohibition is not clear enough to apply, but I believe that God has said recently that it is immoral.
Regarding abortion, we believe that life begins at some point before birth and that therefore, except in cases of rape, or of danger to the mother, abortion is almost as bad as murder. We are not opposed to contraceptives, although a lot of members don't use them.