TL

“Also, if “head” in this verse does equate to source, beginning, or corner stone, then how does that relate to “and the head of Christ is God”? I don’t know of any verses in Scripture that show that God was Christ’s foundation? Or that God is the corner stone of Christ? “

When the Holy Spirit hovered over Mary and caused her to become pregnant with Jesus, that is when God Eloheim was the source or cornerstone or beginning of Christ the Messiah. Remember that Christ is both God and Perfect Human, the miracle that made Him able to suffer death so that we could be saved through His sacrifice.