"As Christians we celebrate the Lord's Supper on the first day of every week just as the Christians did in the first century (Acts 20:7), and like them we do not need a priest to make it possible."
No you don't. So far as I can see you folks have a pretend Mystical Supper. Its no more real than when my two Catholic altarboy buddies and I an Orthodox altarboy,as 9 year olds played Divine Liturgy in my living room, complete with grape juice and Wonder Bread (I got to be the priest because my altarboy robes were gold and theirs were just black with a white surplice.)
You refer to Acts 20:7. We have an actual description of what was going on in those early liturgies from +Ignatius of Antioch, a disciple of the Apostle +John, the successor but one to +Peter as bishop of Antioch. Indeed there is a tradition that he was the child who sat on Christ's lap. At any rate, his Eucharistic theology, from the late 1st, very early 2nd century, makes it clear that the Eucharist occurs only within The Church which is found in its fullness where the bishop is, surrounded by his clergy and laity and centered on the Eucharist. That is where Christ is and thus the Eucharist of The Church is truly the Body and Blood of Christ. He also makes it clear that the bishops are the successors of the Apostles and that they must be obeyed.
Now T, this is about as early as you can get for testimony about what the earliest Christians believed. In fact, his letters are something of a continuation of Acts. He learned from +John himself! I'll grant you that the writings of +Ignatius are not scripture, but they do form part of the knowledge held by The Church, what we in the East and the Latins in the West call Holy Tradition. As such they are part of "what The Church always and everywhere has believed" which constituted the yardstick against which various writings were measured when being tested by The Church for inclusion into the canon of the NT which we all read today. Do you honestly think that The Church, in putting together the canon of the NT would have constructed it as it did so that a proper interpretation of it would contradict everything The Church stood for in its ecclesiology? That's absurd.
The Eucharist may only be celebrated within the body of The Church. We live our lives within The Church as a liturgical people and advance in theosis within a community nourished by the Eucharist which is Christ.
Because all Christians believed that The Church is defined as I laid out above for the first 1500 years of its existence, and those in The Church do to this day, and because that definition requires that the consecrated Eucharist be in fact the very Body and Blood of Christ, if one is in a group which does not have bishops, or better said, bishops within the Apostolic Succession and a "real" Eucharist, one isn't in, strictly speaking, a church at all but rather an "ecclesial community" as +Benedict XVI (whom we Orthodox have the greatest respect for as the elder brother at Rome) so finely put it. Your personal interpretation of scripture in this regard is just that, personal. It is not at all what Christ's Church infallibly believes.