Thanks for your email and happy to hear that my collegevolleyballcoach.com reach goes on the other side the equator and hemisphere. I would be doubly proud if my book, Inside College Volleyball also made it that far south!!
When considering a setter for rally score volleyball, it is about two specifics; delivering a good/hittable set to the hitter, and then making the best choice of which hitter to set. As simple as it sounds, that is all you should be looking for. Rally score games are very quick, and a couple of poor sets or poor choices, can translate into a loss.
Determining who has the ability to deliver a constantly good/hittable ball is relatively easy - Just have them set in hitting lines or position drills and observe how consistent they are.
Determining which setter makes the correct choice is a bit more delicate, and takes review of the player in competitive situations, along with coaching them to make the correct choice.
Of the two, a consistent/hittable is the most important; the wrong choice, but still a good set to a hitter has a chance to be a kill. The right choice of hitter, but a bad set, still has a chance to be a negative attack.
One last point, very rarely do you want to take a good hitter and make them a good setter - Rally score puts a premium on having elite level attackers over elite level setters. Your first concern as a coach is your Outside Hitters who can attack and pass, your second concern is your Libero/DS's to ensure/support your successful passing, then be concerned with the setter and your last concern is probably your MB's - Just find a couple who can block as to establish the defense, and occasionally put away a set.