Bob, you ask different things that would need to be addressed separately. There is what is in the Bible, it pretty much is what I just posted previously in this thread. Other than referring to passages I would show there isn't much more about it from the Bible. The rest is asking about my point of view, while I might answer that it will be distinct from what I can say from passages. I don't try to go very far from what is shown in the Bible for such things, as what to know about God, while I believe God also impresses things on those of us who are believers and seeking things out.
God is just one being.
Isaiah 43:10-11,
“You are my witnesses,” says Yahweh,
“With my servant whom I have chosen;
that you may know and believe me,
and understand that I am he.
Before me there was no God formed,
neither will there be after me.
I myself am Yahweh.
Besides me, there is no savior."
What you asked about in
Matthew 28 is what is shown for the formula for water baptism of confessing believers. The only clue that the Father, the Son, and the Holy Spirit are one being according to what should be said is that the baptism is in the name of the Father, the Son, and the Holy Spirit. Just the one name, and the name is not "The Father, the Son, and the Holy Spirit." The revealed name, shown the most in the Bible as originally written, designated that it is Yahweh.
The Bible shows, in certain places, the heavenly Father is Yahweh, Christ the Son is Yahweh, come in the incarnation, and the Spirit of God is Yahweh. As Yahweh is only one being and there is no other, the heavenly Father, the Son, and the Holy Spirit are just the one being, Yahweh, in their unity. They are never separate in their unity.
I don't really believe the Father generates or generated the Son, that is more from creeds than Bible passages. But the incarnation came from God. Logos the Word, who came in the incarnation, already existed through eternity in unity as one being with the heavenly Father and the Spirit of God. That is the eternal nature of God, plurality in absolute unity. I believe mathematics was eternal in the knowledge of God, and it proceeds from this.
Each is always in communication with the others, in one being. Jesus the incarnation of Logos, with God and being God, prayed to the heavenly Father, not to himself, Jesus. They are one in many senses. That we should be one is not in all those senses. But it is about unity. They each have a will. But the will of each agrees with the will of each other. Jesus as a man in the incarnation still had a struggle with that, but never violated the agreement which continued.
God as one being, still as the heavenly Father, Logos the Word with God, and the Spirit of God, in full unity, is Love, which is only possible through eternity independently of when God produced creation with there being that unity of the heavenly Father, Logos, and the Spirit of God together. God models that love perfectly, as when God made this world, and everything was what God called very good, it was what would be perfect for us, and all life in it. This of God's perfect will is modeled for us, God's love is modeled in that.