When Jesus was a man on Earth, did he cease being God in Heaven? Was there a Trinity prior to the birth? Were there two

[Major Nikon]

9. Not sure where you got those verses from, but at best it's highly edited

Not even the KJV reads that way. I don't know of any serious biblical scholar that attributes John 1 as biblical proof of the trinity doctrine. What most will tell you is that it's been mistranslated through most biblical translations as to remove what it would have meant at the time it was written.

The synoptic gospels contain no evidence the anonymous authors of those scriptures ever were intended to suggest a trinity. What they actually do intend and explicitly say was Christ was the messiah, and the messiah and god are mutually exclusive at least as far as any practicing Jew in the first century would have perceived those two entities. The reason the concept of the trinity is vague and confusing is because the biblical evidence for it or even any reasonableness is non-existent. As you allude, it was a doctrine formed centuries after the death of Christ.