sayings

perhaps yes
I think yes...but "singing to the choir" phrase but is not something I can say I've heard. I think it is someone mis-using the other phrase.

Singing to the choir is not a standard expression. Never heard it used. Can't say what it means.

On fine spring Sunday mornings, attendence at church has been known to be very sparse.

Whatever the rest of the faithful are doing, the preacher and the choir have a reason to attend. In fact, the choir may be the preacher's only audience.