Another important principle, shared by all of us, I think, is that you use Scripture to interpret Scripture. Though presented in the words of many human authors, Scripture is essentially one work with one Divine Author. So you can go from cover to cover, from Genesis 1 to the last words of Revelation, to find the full dimensions, the depths and heights, the ramifications and implications of the particular passage you are studying.
We're agreed on this, I think?
OK, as for Revelation 12: It's not just "the Catholic Church" that says this is a Great Sign: the passage itself says its a Great Sign. The passage itself says this is the Mother of the Messiah (because he Son, the one who "rules the nations with an iron rod" is identified as the Messiah in Psalms 2; the one "snatched up to God and to His throne" is likewise Jesus, and is an image of His ascension.) All his fortifies the identification of the woman of the Great Sign with Mary, since as we know from the Gospels, she is the mother of Jesus.
A third image is that this Woman of the Sign, and the Dragon, are enemies. This sends us back to Genesis 3, where we read that God said to the Serpent, Satan, that the woman's seed would crush his head. It is Jesus Christ, the Incarnate Word, who ultimately cruses Satan and is the victor over sin and death. Once again we have the woman identified as Mary, since she is the mother of the Incarnate Word: Christ is her offsprng, the seed of the woman.
Interestingly, the passage refers to "the seed of the woman," but not to the "seed of the man." This is the earliest trace of the prophecy of the virgin birth.
This is the symbolic and moral interpretation of the images in Revelation 12. There's yet more levels of meaning: there's the sense in which this Great Sign, this woman, this virgin mother of the Messiah, is also Daughter Zion, which is to say the people of Israel; and Lady Ecclesia, which is to say the Church.
I think you'll agree that Biblical symbolic language is often multivalent: it can have different layers of meaning that become apparent only at different historic epochs. The Bible makes tremendous use of polysemy, the coexistence of many valid meanings --- usually related, overlapping meanings --- for a word or phrase.
Not when the prophecy is clearly allegorical. If Mary were clothed with the sun she would burn up. The moon under feet would be problematical from an astronomic standpoint much less the weight of twelve stars on her head. This was a new revelation given to John and any reference to Mary would be a footnote else we lose focus of the real meaning of this prophecy. There are plenty of examples of a church being represented by a woman in the Bible if one chooses to look though.
Peace be to you