Those are some good questions, I hope I may be of some help. I am going to start with your last question about the possibility that there were "deficiencies" in the Bible. We believe the bible to be the word of God as long as it is translated correctly. After Christ organized his church, gave the priesthood authority to his disciples, he ascended into heaven after his crucifixion. Then one by one the apostles were killed, thus the priesthood authority was taken from the earth. Then men changed scriptures to suite their needs. I know that the Book of Mormon contains the fulness of the gospel in the way it was set my God, no one to take from or change. The institution of the sacrament is presented in the Book of Mormon, and the proper way to administer it. Also the proper way to baptize is in it. We believe God's words do not cease, he will continue revealing his words to us. It doesn't end with the Bible. I'd encourage you to read from the Book of Mormon, then pray, and ask if the book is True. I am certain you will receive the same answer I did, so long as you ask with a pure and honest heart! Also pertaining to your question about being saved, God will judge every man according to the desires of his heart, but Baptism by immersion, by the proper authority is essential to receive the kingdom of heaven. I sure hope this helps!