Hi, P101,
Let me address what I can and hopefully others will join in and,at the end of the day, we look at what we have…
For simplicity, I have grouped some of your statements together to conserve space. So, let’s see what we have …
One Church In All Ages
There was one Church in Old Testament times, there is one Church now in the present dispensation, and there will be one Church in the millennial dispensation, and all the members of the Church in all the dispensations constitute the one Church.
There have been those who have denied these truths concerning the Church and I would challenge you to explain why the church did not start before AD32 or whenever one would want to say that the Roman Catholic Church actually did start.
So much depends on being exact when we use words - and while I think I know what you talking about… problems immediately develop when assumptions like this are made.
So, let’s take a look at ‘Church’ as identified in the Catechism of the Catholic Church and see if we can work with that:
751 The word “Church” (Latin ecclesia, from the Greek ek-ka-lein, to “call out of”) means a convocation or an assembly. It designates the assemblies of the people, usually for a religious purpose. Ekklesia is used frequently in the Greek Old Testament for the assembly of the Chosen People before God, above all for their assembly on Mount Sinai where Israel received the Law and was established by God as his holy people. By calling itself “Church,” the first community of Christian believers recognized itself as heir to that assembly. In the Church, God is “calling together” his people from all the ends of the earth. The equivalent Greek term Kyriake, from which the English word Church and the German Kirche are derived, means “what belongs to the Lord.”
scborromeo.org/ccc/para/751.htm
So, here we being with the Chosen People as identified in the OT - and we find that the Salvation Plan God has intended for us does not end there. There really is a difference between the OT and the NT - and that difference is the design of God. I really can not answer your question any better than that.
From all eternity, God chose to send His Son, born of a woman, to redeem us from our sins. He first established His Church on earth (about the year 32AD) as recorded in Matt 16:18, promised that He would send the Spirit of Truth to reveal all Truth to us as recorded in John 13:14 - and further, promised not abandon us (Deut 31:6, John 14:18). Then He suffered, died and rose from the dead. And then… a number of interesting things didn’t happen!
St. John writing his Gospel about 50 years after these events - with the ability to see what had already been written - identified not once (Ch 20) but twice (Ch 21) that Christ did more than is recorded here! In short, Scripture DOES NOTcontain everything. And then… there is the First Pentecost - and while quite a lot was written about this - the birthday of the Catholic Church - we find that among all of the Gifts of the Holy Spirit that were so lavishly given - He did not deliver a book or a set of blue prints on how the Church was to run!
Of course, God can clearly get His Message through without having to write it down (Num 22:28). Please note, that when Christ and the Apostles walked the Judean countryside - there was not an official position of Deacon (Acts 6:5). And, as we look at the history of how this position came into being we find that the Catholic Church was growing (developing as some like to say) and the Apostles needed help. And rather than put an ad in the “Help Wanted” section, or whatever 1st Century Classified Advertisements were available to them - they prayed. This is really an important idea, although I am giving it a light touch…

The Roman Empire at the time was a world power concerning agriculture, mining, shipping, building, etc - there was always a need for workers - and based on historical finds (e.g., excavations from Pompeii
en.wikipedia.org/wiki/Pompeii) we find a merchant and tradesman class, guilds - yes, even famous silversmiths (Acts 19:24). The Holy Spirit inspired the creation of the position of Deacon - God gets His message across and does so in his own maner.
So, to conclude this part …

I think using the term ]'Chruch" as you did and as I defined … is perfectly fine. The idea of God forming a Chosen People and Him forming a Church, while one I had not thought of previously, sounds good to me. And, we see the developmental aspects of God’s Plan as it unfolds - starting out with our First Parents, progressing to Abramham and the covenant, then Issac to Moses to the Prophets to John the Baptist - we see God, like a potter putting items in place here, removing items from there until He sent His Son. And, then we have the Church Christ founded - and from this Church we have the NT with the guarantee of God Himself that it is His Inspired Word.
Let me stop there for a bit…
Tom