The Nicene Creed is the only creed confessed during the Mass. The historic rubric omits the Creed "on ferias, and even on many saints days." It is, however, always said on Sundays, and on many principle feasts.
The use of the Anathasian Creed on Trinity Sunday, in place of the Nicene Creed, is contrary to this rubric. In this case, the Anathanasian Creed may be used a the first (OT) reading. Otherwise, it is properly used as a reading at Matins on Trinity Sunday.
The historic rite places the sermon or homily between the Gospel and the Creed. Common usage places the Creed immediately after the Gospel. I would suggest that the placement of the Creed is a matter of local custom.
Since the Gloria in Excelsis, the Creed and the Sanctus share a common dignity; the rubrics direct that everyone faces the (liturgical) East when the Creed is recited.
In those places where the Creed follows immediately upon the Gospel, especially when the Gospel has been read in procession, it is contrary to the rubrics to intone the Creed while the procession is returning to the altar, and while the celebrant is facing the congregation. The sub-deacon returns the book to the celebrant. After the ministers have returned to their usual places, only then it the Creed to be intoned.