Choirs are bout fuckin impossible
but heres some ideas for over-processing sounds for the effect, how Id make a choir without a synth...
Get a nice long female ahhhhh, look in rnb accapellas for the improv moaning parts... Might also wanna grab any other extended phrases you can get from your sampling source, so you can get a few phrases in the same voice.
Go NUUUTTTTSSSS with the chorus into reverbs. But do it all on sends, or using wet/dry's so that the level of effect can be easily maintained and automated.
Layer this, with some OVERLY reverb'd chords of some sort. I find pads tend to fit best, ut Ive had surprisingly appealing results using everything from sitars to pianos, just depends really on what harmonizes best with your vocalist. By overly reverbed I mean reverb to the point of smearing, alot of reverb plugins will have a preset for something like blur or smear or smudge... these are usually a good starting point, but, for this application, thier never svere enough for my taste.
Dont mix your chordage in too hard, very, very subtley, to round you into a key range and to fill out with more sounds.
Group the whole lot of it into a bus, and out to another chorus/verb or two to taste... might also wanna slap a warmer or harmonic distortion or whatever on the final bus. Automate the chorus'es and verbs a bit to taste.
P.S.
Save yourself a headache, and link the chorus send to a peak or even better, envelope+keyboard controller. If your using fruity.
