Concelebration doesn’t need faculties. You only need faculties to be the main celebrant.
And yes, even those who don’t concelebrate self commune. When our bishop led a Liturgy during a meeting of bishops, obviously you don’t shove all the bishops into the altar. So they stayed at the pews (yes, we have pews). But during Communion our bishop brought out the diskos and the other bishops lined up and picked up the Eucharist themselves (not sure if they were asked to line up according to rank and seniority, as is the Eastern tradition).
My bishop and the diocesan vicar for education concelebrated at the ordination of two deacons at the Ukrainian Catholic mission that meets at the local Catholic high school. I asked the mission administrator, a friend of mine, what they did to help the bishop prepare to concelebrate, and he said “We handed him a liturgy book and said ‘Read this!’”
Yup, that is about it. If you ever have the pleasure of serving like I do, you’d be surprised at the amount of chatter that goes on around the altar don’t worry it is not idle chit-chat, but everything is related to the Liturgy. Even from among clergy of the Eastern Church, especially with things like, “okay, you take the next part,” etc.
He’s supposed to vest. If invited to do so, he may serve as concelebrant. If not concelebrating, he should be “vested in choir.” If serving as concelebrant, he should be vested in his Roman vestments. As an economia, the pastor may permit a Roman priest who has not his own vestments to wear borrowed ones local to the parish.
Vesting in choir, for romans, can be Alb and stole or Cassock and Surplice, with the canons giving preference for cassock and surplice.
Note that some travelling priests will simply sit in the nave in street clothing, but properly speaking, a priest who isn’t suspended is supposed to sit in choir.