A Jew once told me that the Messiah being YHWH is anathema to them.
Perhaps. So you should appreciate the horror some Jews would have felt to see OT scriptures referring to YHWH being applied to Jesus. There are scores of these in the NT.
I don't see anything in the OT that says the Messiah was already alive in heaven.
There are not that many OT scriptures referring to a Messiah-figure per se. But there are various scriptures referring to heavenly Wisdom as being pre-existent or being an extension of God that were applied to Jesus in the earlier Church (e.g. Proverbs 8, Sirach 24, Wisdom 7), and there are various texts in the Gospels and the NT that present Jesus as Wisdom (cf. Matthew 23:33-38 = Luke 11:49-51, 13:34-35). See also how the description of Jesus in Hebrews 1:3 and Colossians 1:15 reflects the wording in Wisdom 7:22-25, and how the wording in John 1:5, 9 reflects Wisdom 7:26, 30.
People have bastardized John's prologue (the pronoun is neuter, i.e. "it (the LOGOS) created all things"
I'm not sure what you mean here. The demonstrative pronoun houtos in v. 2 is masculine. The neuter form is touto.
1 Colossians (which speaks of the new creation, not the creation of the universe).
No...v. 15 does not refer to creation as an event per se, but it refers to "all creation" as EVERYTHING in the universe that was created, "all things in heaven and on earth, everything visible and everything invisible" (v. 16). The "new creation" is here not in view. Verse 17 also states that he existed BEFORE "all things" existed.