I'm not sure if the A320 would require any serious retraining. F9 pilots, IIRC, are trained and certified for the A320 family in general. There isn't an A318 simulator, an A319 simulator, and a A320 simulator - there is just one A32X series simulator and subsequent rating. I believe that any pilot rated for the A320 can fly the A318, 319, 320, and 321. I'm sure the situation would be similar for the flight attendants as well. If the previous statements are incorrect, I'm sure someone will be more than happy to correct me.

What may change, however, is the number of flight attendants on board. If the A320 configuration is similar to that of Jet Blue, than there will be 150 seats on the plane. The law requires only three flight attendants for 150 pax, but F9 may increase the number of F/As to four, just to help with service. I'm trying to remember how many F/As are on Jet Blue's A320 flights.