That’s a trick question. :-)
There is a difference between praying for someone and praying to Mary (who is in Heaven) to intercede for you. The first one is clearly biblical but the later is not.
You said intercession. We are commanded to pray for one another, and we can ask Mary, who is in heaven, to pray for us, just as I can pray for you, or you can pray for me. This is all that is meant by intercession.
You are very right that we are not to pray TO Mary, but we can ask her to pray for us sinners, which is exactly what Catholics do when they pray the Rosary.
“Holy Mary, Mother of God, Pray for us sinners, Now and at the hour of our death, Amen.”
Much of Catholic Mariology is derived from Sacred Tradition and rpedates Scripture. The idea that all revealed truth is to be found in "66 books" is not only not in Scripture, it is contradicted by Scripture (1 Corinthians 11:2, 2 Thessalonians 2:15, 2 Thessalonians 3:6, 1 Timothy 3:15, 2 Peter 1:20-21, 2 Peter 3:16).
Sola Scriptura or the notion that all of the Revealed Word is contained in the Torah is a concept unheard of in the Old Testament, where the authority of those who sat on the Chair of Moses (Matthew 23:2-3) existed. For over 400 years, there was no defined canon of "Sacred Scripture" aside from that same Old Testament; there was no "New Testament"; there was only Tradition and non-canonical books and letters. Scripture was defined from the many competing books by the very Tradition and Apostolic Succession denied by Protestants as being non-Biblical.
Celebrating Christmas on December 25th... not biblical by the same standard.