Job 38:4-7 “Where were you when I laid the foundations of the earth? ... When the morning stars sang together, And all the sons of God shouted for joy?"
"Morning stars" and "sons of God" appear to be references to angels. (One could debate this, of course.) If they sang and shouted when the Earth was created, and according to Genesis 1 the Earth was created before humans, then the angels must have been created before humans.
Satan tempted Adam and Eve in Genesis 3, and as you mention there's the reference to an angel standing guard at Eden. So if angels were created after humans, it was not long after. Not more than one generation, anyway.
Christians generally interpret the "let us ..." statements of Genesis 1 as the persons of the Godhead speaking to each other, i.e. Father, Son, and Holy Spirit conversing among themselves. There's no indication of angels participating in creation or of humans being created in the image of angels, but both Father and Son are described as creating, so this generally makes more sense than supposing that the "we" means God and angels. (I'm not sure how Jews interpret this.)