The correct answer I think will depend upon the size of the church and its congregation. The larger the congregation the larger the talent pool. I recently left a praise team at a church with 1200 or so persons attending 3 services on Sunday. This church had rules,,,if you want to sing you will rehearse. We had 7 persons singing with backups in all but the tenor. In my current church we are a start up church one year old.. We have a small congregation but are blessed with a four person praise team of great talent and dedication however it is difficult for all to make rehersals or even to have rehersals. This presents another problem..we do not have a great talent pool. So we must take it as it comes so to speak. What I am trying to say is that you have to start in one place and grow. Ultimately you need to find only a remnent, a few dedicated souls and then establish rules for all to live by. If your church is large enough,,,establish rules and stick to them,,,no reherse no sing. If not,,,move slowly towards that place by expanding your praise team and band. But by all means,,,make the music great,,,and great things will follow.