I usually agree with you, Tom, but not here. The Twelve did not have the indwelling of the Holy Spirit at this time, which I think is one of the marks of the Church, in the sense that it is the church of Jesus Christ.
After all, look at how they scattered when Jesus was arrested and how Peter denied Jesus. But look at how they persisted, preached, and endured imprisonment and even death once they had the indwelling Holy Spirit.
I do not think the church of Jesus exists without its members (believers) indwelt by the Holy Spirit, which is also why I do not think the assembly in the OT was the church.
Marcia, you and I are approaching this question from different directions, so as long as we make our cases from those different perspectives, we'll likely talk past each other without success.
With regard to the Holy Spirit at Pentecost, you see it as indwelling, I see it as empowering. I do agree that the HS indwells all believers, but don't see this as critical to the definition of the beginning of the church.
I contend that the church Jesus established during his earthly ministry had everything the churches of today have. It had a Head, it had an organization, it had a commission (see Mark 3), had a message, the disciples were ordained, they baptized, and it had the Lord's Supper. They had power over demons, they could heal the sick. And they had instructions regarding discipline in the congregation.
The source of their power was Jesus himself. When he was about to leave them, he told them to wait, and they would receive power again. It came, at Pentecost. The band of 120 huddled in an upper room suddenly became bold and fearless, even to death.
The other point is that the Twelve, the material of the first church, assembled. Churches assemble. The church at Jerusalem was empowered while it assembled. It assembled constantly for the study of the Word of God and for fellowship and worship.
The Great Commission was given to the eleven, while they were assembled, a church, if you will. The same commission is meant for each succeeding church that followed.
I also hold that the concept of the Universal Church, made up of all believers, is a fantasy. The New Testament knows nothing of any other kind but the local congregation, except when it speaks in a generic or institutional sense, in the same way we speak of the family.
So, I suppose we are both being consistent, given our pre-suppositions. The fact that they are different will make it difficult for us to see things the same way.