I thought I would address this part more specifically:
Since you said "only in the Gospel of John" - I thought I would look at the book of Matthew:
Matthew 1:23 Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us.
Here Matthew recognizes him as God.
Matthew 3:17 And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
Apparently, someone in Heaven thought so.
Matthew 4:3 Then the tempter approached Him and said, “If You are the Son of God, tell these stones to become bread.”
The tempter recognized him
Matthew 8:29 Suddenly [the demons] shouted, “What do You have to do with us, Son of God?”
Demons recognized him
Matthew 14: 33 Then they that were in the ship came and worshipped him, saying, Of a truth thou art the Son of God.
Jesus certainly didn't have a problem with people calling him the Son of God.
Matthew 16:15-17 “But you,” He asked them, “who do you say that I am?” Simon Peter answered, “You are the Messiah, the Son of the living God!” And Jesus responded, “Simon son of Jonah, you are blessed because flesh and blood did not reveal this to you, but My Father in heaven.”
Jesus acknowledged Peter's statement as not only true but revealed by the Father
Matthew 27:54 Now when the centurion, and they that were with him, watching Jesus, saw the earthquake, and those things that were done, they feared greatly, saying, Truly this was the Son of God.
A Roman understood.
So, it is pretty much everywhere and confirmed by a multiplicity of venues.
I'd like to see this in the original Greek with translation notes