"Am I correct in saying the Orthodox do not hold to many of the RC Marian doctrines and purgatory, as well as in the Eucharist, the host and wine become 'grace filled', rather than transubstantiated into the actual blood and flesh of Christ?"
Orthodoxy does not accept the Latin concept of purgatory, nor do we accept the Latin dogma of the Immaculate Conception (Otto, this is a very, very complex theological subject). I am not sure what other Marian doctrines you might be referring to. We absolutely believe that the bread and wine consecrated at the Divine Liturgy, through the actions of the Holy Spirit, do indeed become the actual Body and Blood of Christ. It is, however, a Mystery to us and therefore we do not attempt to explain it nor do we use the word "transubstantiation".
Thank you for witnessing to your faith.
If I offended in my questions, which you did not mention, but if I did, I apologize.