When there is true fellowship with God, it comes natually. The power of Christians does not come from human cooperation but from life-union with God. Let barriers be removed as we can. Faith is the gift of God which produces in us this fellowship with God in Christ. It cannot be created or maintained by human efforts.
Faith is but another name for fellowship.
None of them can be the center. There was a time when this was the church at Jerusalem - Antioch, etc. The church at Corinth was plagued with disorder - the churches in Galatia, etc. Paul speaks of the occasion when the whole church at Corinth comes together in one place. Church fellowship seems impossible apart from an intervention from above.