When considering how many singers to put on stage with your Worship team, think about these things:
Do I want intimacy or impact? Intimacy usually calls for fewer singers.
Harmony often dictates style. A Hillsong United sound will probably not have three part harmony, whereas southern Gospel usually requires at least three parts.
What can your sound system handle? Many parts and many voices require a higher end system to guarantee all of the parts will be heard.
How skilled are your sound technicians? Can they clearly distinguish one part from another? Do they know how parts should be balanced?
Are you willing to boost the instrumental volume to support more voices? One of my pet peeves is a sound mix that has the voices blaring so loud that the instrumental mix is lost. Harmonies don’t sound right if the instruments are too quiet, unless you are singing a cappella. In that case, who cares.
How much instrumentation are you using? I love doing acoustic sets every now and then, but an acoustic set requires a minimum of everything, including voices. Otherwise you end up with a vocal ensemble and obbligato instrumentation.
The point is that harmony should be an intelligent choice, not a given. Contrary to some Christian thought, God is not present in proportion to how many singers you have on the stage.
How many singers do you use on a given Sunday, and why?