About #3.
There is one God. God is three persons in one (Father, Jesus Christ the Son, and the Holy Spirit). This is a mystery. It is not contradictory. It certainly is not polytheistic.
We do recognize that angels, Lucifer and his demons exist - the Bible indicates that they are all God's creation. We do not worship any of them but we do recognize that they exist and take action in the world.
I can't say anything about the Virgin Mary and Catholicism. As a protestant, she was Jesus' mother, a chosen person. Now she is dead and is in paradise but that doesn't mean that she answers prayers or should receive any prayers, in the same way that would apply to Moses or the apostle Paul.