It's not a metaphor because in the chapter as well as the other chapters it emphasizes and textually confirms and identifies the red dragon with the same serpent from the Garden and the names Satan and Devil, it's a positive identification within the text itself. Then going to Genesis 3 to cross reference it we find the same description as a serpent, which can also mean a dragon in ancient tongues, as well as how he got those names. Devil because that's the first sin, the Lies, and then Satan because God cursed him with Enmity with man. And also Satan's doom is woven into our salvation and the prophecy and PROMISE, ergo Word of God, to have Jesus born of the Vrign Bride to defeat the Devil's kingdom.
In terms of the Morning Star, the Morning Star is just what it is the literal morning stars in the dawntime ltieral sky that can still be observed in the sky to this day, i nespeciality the primary Mornign Star that our culture calls it Venus. The morning stars are featured directly singing in the courtyard of the heavens to God in the book of Job. The Morning Star is an epithet of the Bible (as well as Near East ancient cultures) likening to someone being bright, a herald of the dawn, intelligent, wise, etc. This epithet is applied to the King of Babylon in the book of Isaiah, likely Nebuchadnezzar, and indeed our Lord and Savior and guiding light Jesus Christ in the book of Revelation. The Morning Star additionally is one of the spiritual tools/weapons given to those that hearken and overcome Jezebel's Spirit and refuse to commit or condone fornications, adulteries, and idolatry in the letter to the Spirit of the Church of Thyatira in the book of Revelation. Praise Jesus he is the bright and morning star!