There is a total identity of faith between the prophets and saints of the Old Covenant, and the same in the New. The only difference is the first lived in anticipation, why we live in realization. If the Jews did not follow Jesus, so many could hardly have been looking for the consolation of Israel at the time of His birth, as we know they were.
If the Holy Maccebees did not follow Jesus, we could hardly have a feast in their honor on August 1.
a Jew, he believed that "burnt offerings" atoned for our sins, dead or alive
No, as a true believer, he believed that God had ordained them as an outward ritual to express inner contrition over sin. Where the Prophets rejected "sacrifices and sin offerings" they were doing so where man had made them an empty formality, not because Jews were not really bound to fulfill the law. Jesus Himself fulfilled the law and slaughtered many sheep for the Passover and other feasts, to say nothing of the sin offerings for His Most Holy Mother at the Presentation, etc.
Thus, the circle closes: the belivers who repeneted are forgiven; the sinners who didn't are not
This seems to me to reject the distinction between serious or mortal sins, and personal faults or venial sins. We believe God cleanses us of our minor personal faults still remaining at death after death so that we might be without spot or blemish, since few of us are perfected entirely here on earth. But those who die in actual mortal sin are condemned and without hope.
Furthermore, the Cathechisms of the Orthodox Church, while stating that prayers for the dead are good (prayers are always good!) say very little beyond that, and I agree with that.
Your explanations on the Immaculate Conception seem equally reasonable, however, if the HVM was given a soul full of Grace, she was unlike any other human being and therefore not someone we can call our own.
On Macabees, is there any source that specifically says Jesus or His Mother actually slaughered sacrifical animals, as you seem to imply? Sacrifice, remember, is not required.
As for St Mark of Ephesus, I believe Agrarian is right in asserting that he was trying to find a "working formula" in order to satisfy the Emperor's desire under duress, but remember that no Father individually has monopoly on what the Churches, as from what I gather from Orthodox Catechisms the Church is silent on what happens to them while asleep in the Lord, except that they foretaste the bliss.
"If the Holy Maccebees did not follow Jesus, we could hardly have a feast in their honor on August 1."
We commemorate in Orthodoxy a number of OT figures. The fact that Rome has a feast day for the Maccebees obviously has meaning for Latin Christians, but it wouldn't for Orthodox Christians.
"This seems to me to reject the distinction between serious or mortal sins, and personal faults or venial sins. We believe God cleanses us of our minor personal faults still remaining at death after death so that we might be without spot or blemish, since few of us are perfected entirely here on earth. But those who die in actual mortal sin are condemned and without hope."
Orthodoxy makes no distinction or hierarchy among sins. I may have mentioned before that the Greek word for sin is "amartia" which means "missing the mark". The mark we aim for is to become like Christ.