"Is not" simply shows they are distinct. If the Father is the Son and is the Holy Spirit, then there is no distinction at all.
Again, ontologically. You are saying that the resurrected Christ ascended to exist outside of time. But the manner in which the Bible states they have coexisted for all eternity past is that there never was a time when the Son did not exist as distinct from the Father. This is prior to all creation. In what you are saying is there was a time when the Son did not exist.
Your verse does not at all substantiate your position. You have to go right to the meaning of "only begotten," which I have provided more than once in this thread, only for the crickets to respond.
John 3:16--"he gave his only begotten Son"-- and 1 John 4:9--"God sent his only begotten Son into the world"--both show that the Son was begotten before all creation, before all time and space. And this is precisely what John 1:1 shows, along with verses 2 and 3. This is why we speak of the Son being eternally begotten or eternally generated.
You are conflating two ideas or rather periods of "time"--before all creation of time and space, and after all creation, specifically after Christ's resurrection. John 1:1-2 show that the Word, the preexistent Son, existed alongside and in intimate relationship with the Father prior to the creation of all space and time, before the beginning began. This is further supported by verse 3:
Joh 1:1 In the beginning was the Word, and the Word was with God, and the Word was God.
Joh 1:2 He was in the beginning with God.
Joh 1:3 All things were made through him, and without him was not any thing made that was made. (ESV)
Simple logic tells us that since "all things were made through [the Word], and without him was not any thing made that was made," then the Word has always existed, in intimate relationship with the Father. If the Word came into existence at a point in time, then John 1:1-3 are false.
1 Cor 8:6 and Col 1:16-17 simply repeat the simple logic of John 1:3. And notice that neither mention the Word, but rather 1 Cor 8:6 says "Jesus Christ" and Col 1:13 tells us that Paul is speaking of the Son in verse 16 and 17.
If you were, then we wouldn't be having any disagreement. Do you agree that there was a "time" before creation existed, that all that existed was God? If so, did God exist as three coequal, co-eternal, consubstantial persons? If not, then you are not in agreement that God is ontologically three persons.
If by "same Spirit" you mean "same substance," then yes, but that language is confusing, as it sounds like the Holy Spirit is all that exists, who also happens to be the Father, who then came in the flesh as the Son. But that is not biblical.
This is stunning but not surprising. I have addressed this error several times in this discussion ('echad and heis vs. yachid), only for every anti-trinitarian not only to ignore it, but to then repeat the same defeated argument. Again, this is only a statement of monotheism, not a statement regarding the nature of God. You would do well to stop using it to support your position, because it doesn't.
If you don't agree with the Athanasian Creed, then you really believe in three modes, not persons. Or, if you believe one eternal Person became three Persons, then that would also be three modes, not persons. Distinction of persons in that case is just illusory or superficial.
Because the historical doctrine of the Trinity, being based entirely on Scripture, fully affirms monotheism.
No, it's just to keep them distinct and, as the Athanasian Creed states, to not confound the persons. That is, to not say that the Father alone existed for all eternity prior to creation and then became the Son and the Holy Spirit. Or, put another way, to not say that one Person became three Persons.
Because it doesn't, otherwise it would completely contradict the NT.
Yes, he is truly God and truly man. That is in harmony with the historical doctrine of the Trinity.
Jesus is the Son come in human flesh. That is precisely what John 1:1-3, 1 Cor 8:6, and Col 1:26-17 clearly show. Logically, it cannot be otherwise. As I have also pointed out many times in this discussion, Jesus said that he came from the Father, that he was sent by the Father, and that he was with the Father prior to his incarnation (John 3:13; 6:38, 62; 17:5, 24). These ideas are then repeated in various places throughout the NT.