If you have a group of singers that are "learning" yet are required to sing every Sunday, then I suggest sing some songs unison. Its not ideal, however, it allows the choir to sing fresh songs while working on other material. In addition, I have found that if you have a strong singer with ad-lib abilities, that will ad some spice to the song. Overall, this strategy allows you to develop choir members vocal challenges as well meet the your weekly singing obligations in a presentable manner.
Be realistic about your song choices. Know the strengths and weaknesses of your choir. If its a small choir you should know the strengths and weaknesses of each individual. If your choir has trouble memorizing songs, choose songs with minimal lyrics.
You have to plan. Nuff said.
Stay positive and realize that this is a process. You are watering a seed. Evaluate after a few months and make adjustments as you see needed.