Im trying to understand the Book of Mormon. In Jacob the Lord says that taking many wives is an abomination.?

Why did Joseph Smith and the other Prophets after him practice this until 1890? Also, I haven't read the entirety of th BOM but what is the significance of the Doctrine and Covenants. Shouldn't the BOM be enough and does it state in the BOM that there the Doctrine and Covenants is of God?? To me that is where everything gets really weird and it seems more as if Joseph Smith is starting his own church especially knowing that the Temple Ceremony is the same as the Freemason's, that doesn't seem very original or that it was a revelation if Joseph Smith just took what the freemason's were practicing and called it a revelation. And also, what about the references to steel, ox, cows, horses and goats when archeologists haven't found any remains that date this far back?? Im really trying to figure all of this out and would love to read the BOM and not questions these facts. Can someone explain? I know there are a lot of questions- thank you