The RB lenses are super for portraiture, the transitions are typically very smooth.
The newest KL lenses have, in my opinion, better colour neutrality. I suspect that it's more than coatings that distinguish the KLs- I think they are better colour corrected. And note that if you shoot b&w, dispersion does still matter.
I'd advise going with the newest pro SD body and KL lenses if your budget permits. The price difference between new and much older (and probably heavily used) RB gear is typically small (at least compared with their main competitor, the hassies).
The standout lenses, to me, are: the 65 KL, the 127 KL, the 150 SF, and the 210 KL apo, the latter being quite possibly the best all round lens in the system.
Consider getting a motorized 6x8 back as well. And if you aren't familiar with bellows factor, a metering prism will be a welcome tool. The RB is such a weapon for closeups, and a metering prism really speeds you along.
P.S. I've had no issues at all with the KL shutters, and I don't see why I should expect any. The RB system remains the most rock solid system on the market, bar none.