The roast in my cook was a 16.5 lb roast and I cooked it in the rotisserie at 225f indirect for six hours to an internal temp of 130f. I actually closed the vents down a little more three quarters of the way through the cook because I was a head of schedule. For my liking no further sear was needed. If I did need more of a sear I would remove the rotisserie basket remove the deflector and reinstall the rotisserie basket.
As MK1 says the rotisserie is not necessary because of the convection cooking in the KK but its so cool to spin cook a prime rib in my opinion.
No matter what you decide I'm sure it will be perfect.