I can't give any specifics on mic selection for rear-mount, but I find that a cardioid mic mounted near the front aimed toward the congregation provides better ambience of congregational singing (just try standing near the front when they're singing, then compare that to standing in the back and you'll see what I mean) as you will get more direct vocal sound. Positioned in the back, much of the sound picked up by the mics is reflected. By using cardioid mics, you can minimize the amount of sound from the stage (which should be picked up by on-stage microphones anyway) and loudspeakers picked up by the mics.
It has been mentioned that there will be a time delay effect of rear-placed microphones as direct sound from the stage mics will be followed shortly by direct and reproduced sound from the ambiance mics, due to the time it takes for sound to get from FOH to the mics. Placing the ambiance mics near the front pointed toward the congregation minimizes this effect, but you still get the reflected sound which is what makes it sound like you are in a large room rather than an acoustically dead studio. However, front placement WILL increase the noticeability of crowd noises such as talking and coughing.
Yes, even though it sounds like you've pretty much settled on rear-mount, I'm still advocating for front mount. I firmly believe the results will be more pleasing.