Mark Brymer has done a beautiful job with this arrangement. As with any piece so well known as “River of Dreams,” the quality of your soloists will make or break it. Choose them carefully.  And then rehearse your choir so they can be comfortable in the backdrop role. You’ll need to decide how to handle the glottal stop (h) as this will change the feel. I’m going to experiment with it…. using a softer approach in the beginning and then allowing the choir to come on stronger at the end, using the glottal stop for emphasis. The rhythm is complex and changing; this is the hardest part for rehearsal. Use dynamics to keep the energy high.  Your choir and the audience will love this piece.