Dear katholicos,
Yes, we agree on the Assumption, the perpetual virginity and upon venerating her as the Theotokos. The first two however, are not doctrines; the Orthodox Church tends to go in for dogmatic statements rather rarely.
On Original Sin the difference seems, to us, to be this. Rome seems to us to hold the Augustinian view that mankind inherits sin as part of its nature because of the Fall; we all inherit the taint of sin. This is not how the Orthodox understand these things. For us, mankind is made in God's image, and whilst that image was marred by the effects of sin, we are not inherently sinful; we are influenced by the sin in this world where sin holds such sway. But this is a marring of the image, which through baptism and chrismation, we can begin to clean away through His Grace, and which, through the Eucharist and the other sacraments, and through living the Christian life, we can further clear away through a process we call theosis or divinisation.
This being so, we see no need to argue that the Virgin was born without sin, for we are all born without it; but she was, like the rest of us, born into a sinful world. We would hold her behaviour all the more meritorious because, although she could have fallen into the temptation of sin, she did not. If she had been unable to sin, where would be the merit in her not sinning?
Hope that helps a little.
peace,
Anglian