Dick, he says ... it is not new songs, or song books I am asking about here.
I songlead every week in church. Most of what I present is not familiar to our people, but the formulas of the tunes are certainly simple. Not praise music-- oldtime gospel, revival hymns, bluegrass gospel, spirituals-- all forms of gospel, including black and blues.
What I find matters most is my own willingness to transmit the song--my attitude that I will certainly not do it perfectly or at a performance standard, but enough to get the tune across. I don't teach anything of the new songs at all, in any way. I just direct their attention to their songsheet, strum out a rhythmic intro on my autoharp, and go for it. By the time the first verse and chorus are done, they are singing right along.
I don't want them to act like a choir, rehearsed. I want them to act like they are singing along in the privacy of their car, at the top of their lungs, having a great time. They see that the song does not scare me, so it does not scare them. Believe me-- this has worked with every group I've led, whether it be in church at our informal Saturday night service, or at the old folks homes, or with kids.
The only time I teach any of it is if I am doing a spiritual for which they have no songsheet-- impromptu paperless songleading where the call/response pattern showes the people their part. I will decribe the pattern briefly to let them know what to listen for, then launch in. I point to me on my part for the first few verses, and point out with open arms & raised hands when it's their part, till they seem to have it. (I can tell they have it when I start to hear them join in on my part too, adding harmonies or exclamations, or if a few start clapping, or if I see them starting to sway.) Just between you and me, I don't think the description really helps them-- but they are Episcopalians and they sometimes think they need a little structure to start from.
Doing mostly the tunes people recognize makes sense for your situation, but what I have learned from NOT doing what people already know is, it's not me-- it's the song. I think the biggest challenge you will have, using as songleaders people who work hard at being technically good singers, is that they must loosen up, be quite unprofessional, and think of themselves as entertainers rather than performers when they put on the songleaders' hat. They have to sing informally enough that people will not be shy about singing along with them.
I used to sing in various levels of community choirs and I have a nice, clear, high soprano. It's no use to me as a songleader though. For that I find that I use more of a musical-comedy-stage voice. Frankly, it is very hard on my voice to sing in that range and with that kind of expression, staying in the middle-lower end of my range below the head-voice breakpoint. But the people don't sing in my range, and I have to be able to belt out the tune well enough for them to hear me above themselves and each other, unless it is a tune they know better than I do.
So in terms of technique, I would go to your mezzos and tenors and let the ones who can really belt out a solid line of melody take this project on, one at a time as they demonstrate they can get past the learned choral technique and have a good time as individuals, and then group them into 3-4-somes. They can practice (audition) on the rest of your choir! :~) In fact if I could practice on our usual Sunday 10 AM choir, I think I could get them to relax and have a WHOLE lot more fun! Thanks for the idea!