I would really like to believe in the Christian myth but I do not see any OT justification for the doctrine of Atonement. Any authority for the idea of a Hebrew Messiah comes from the Hebrew scriptures.
The doctrine of atonement is contained in the sacrificial laws of Leviticus. As you have noted, these laws called for the sacrifice of animals, not humans.
This verse specifically calls out a Day of Atonement to be observed annually.
26 And the LORD spake unto Moses, saying, 27 Also on the tenth
day of this seventh month
there shall be a day of atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the LORD.
The Holy Bible : King James Version., Le 23:26-27.
1) Jehovah says that human sacrifice is acceptable.
He does not say this. He says the opposite. In The following verse he specifically condemns the practice of human (child) sacrifice that Israel had begun practicing in imitation of some neighboring tribes.
16 And they left all the commandments of the LORD their God, and made them molten images,
even two calves, and made a grove, and worshipped all the host of heaven, and served Baal. 17
And they caused their sons and their daughters to pass through the fire, and used divination and enchantments, and sold themselves to do evil in the sight of the LORD, to provoke him to anger. 18 Therefore the LORD was very angry with Israel, and removed them out of his sight: there was none left but the tribe of Judah only.
The Holy Bible : King James Version., 2 Ki 17:15-18.
2) Jehovah says that one person may atone for the sins of another person.
He does not say this. However, in the case of Christ, it was not a mere man providing the atonement. Rather it was God himself working through his person of Jesus.
If you are interested, the Book of Hebrews provides a detailed explanation inthe context of the Old Testament.
3) Jehovah says that an individual is not responsible for his own actions.
He does not say this either.
4) Any place where Jehovah holds humans to the standards of perfectionism.
He holds them to the standard of perfection in that they will worship him only. Worship directed towards anything else is unconditionally condemned.
Beyond this he gives them a moral code of conduct and expects them to follow it. However, he recognizes their imperfection and forgives their transgressions if they turn to him in repentence. This is seen in many places in the Old Testament. The story of David is prominent and the Psalms are replete with this theme.
5) The principles Jehovah established quite clearly in EZK 18 are made invalid.
Ezekiel 18:21-22 below demonstrates what I said above. If a wicked man turns from his sins in repentence then God will forgive them and will not remember them at all.
21 But if the wicked will turn from all his sins that he hath committed, and keep all my statutes, and do that which is lawful and right, he shall surely live, he shall not die. 22 All his transgressions that he hath committed, they shall not be mentioned unto him: in his righteousness that he hath done he shall live.
The Holy Bible : King James Version., Eze 18:21-22.