Second, tell me how the foundation consists of apostles as the "first" set in this body (Eph. 2:20; 1 Cor. 12:28) and yet even though you believe "not many" were placed in this body prior to Christ's earthly ministry how is it they are not "first" or at least the Old Testament "prophets" are not "first" to be set in this body?
The term "first" is reference to the revealing of the Body "first" to the Apostles directly from Christ, which includes Paul on the Damascus road. Then to the world via the Apostles, and I believe the "prophets" includes OT and NT prophets, but not many commentators I'm familiar with refer to "prophets" here as exclusive to the NT prophets.
I believe it is meant that "the foundation of the Apostles and prophets" is Christ, and not these, who are built upon Him; Christ is also, as we know, the "primary corner stone" (Eph 2:20).
Another example: "And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb." (Rev 21:14). "Because He has been ministerially laid as the foundation, by the twelve apostles, for men to build their present and future happiness upon, therefore the foundations of the wall of salvation are said to be twelve" (Gill).
I believe the present dispensation began revealing the Body, and since this includes all Heavenly dwellers, it means all who are and will be there.