The Preparation is actually not a part of the Mass liturgy. If it the custom of the parish to use a separate Confessional Service before Mass, it need not be included.
The Introit is the beginning of the Mass liturgy. According to the historic Western use, the Introit is not begun until the celebrant and ministers have come to the altar. Having made the customary reverence - the celebrant kisses the alter at the midst, and the deacon where he stands at the right of the celebrant - the celebrant (or Kantor, or choir) intones the Introit of the day.
Although local customs may vary, beginning the Introit only after the ministers arrive at the altar is to be preferred, especially if it is customary to incense the altar during the Introit. Everyone will already be in place, able to complete the incensing while the Introit is being sung.