Story: So in a sense everything I decide and do was predetermined but it's still down to my free will. [/quote]
No, God does not decide for you what color socks you must put on. We FREELY make our decisions, but God can influence and thus controls OUTCOMES.
Story: My future was determined by me before I even existed. Maybe I've always existed.
Your future as far as what? Salvation? As far as salvation, what God predetermined were the choices (accept vs. reject Him) and the consequences and destinations for each choice. But He did not choose person A will be saved and person B will go to hell - although He has always known their eternal fates, as He is ALL-knowing. Each person chooses their own fate per their final response (while living) to God / Christ.
Story: God cannot change, right? So if I've not always existed doesn't that change God?
How so? As everything was created by God!
"For by Him all things were created that are in heaven and that are on earth, visible and invisible, whether thrones or dominions or principalities or powers. All things were created through Him and for Him." (Colossians 1:15-16)
Story: Energy and matter can transform, I am energy and matter now, maybe death is just matter changing to energy.
Sounds like your being influenced by New Age thinking? Christians will have PHYSICAL bodies - albeit spiritual, non-corrupted, transformed ones in the New Heaven and Earth. Jesus was PHYSICALLY resurrected, as all Christians will be - their spirit already with the Lord will unite with their eternal resurrection bodies. The new Heaven and earth described in Scripture is of a physical place, as the Apostle John writes He actually SAW:
Revelation 21: 1 "Then I saw a
new heaven
and a
new earth,
for the first heaven and the first earth had passed away, and the sea was no more. 2 And I saw the holy city, new Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. 3 And I heard a loud voice from the throne saying, “Behold, the dwelling place[a] of God is with man. He will dwell with them, and they will be his people,
and God himself will be with them as their God."
1 Corinthians 15: 51: "Behold! I tell you a mystery. We shall not all sleep (our former bodies dead), but we shall all be changed, 52 in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we shall be changed."
And do not make the error of belief in "soul sleep": https://www.gotquestions.org/soul-sleep.html