Well, there's a whole lot of ways to work this..simply put :
- you'll need an appropriate rehearsal/recording space (critical, don't just settle for anywhere)
- you'll need a variety of good mics, mic stands/booms, a console, playback systems (both headphones and monitors), cables, distro boxes, duct tape, tampons, electronic tuners, blankets...
- a mic'ing strategy
- all of the instruments (especially the drums) need to be checked for rattles etc.
- drums/percussion need to be tuned
- piano needs to be tuned (about a week ahead of time)
- recording space needs to be checked for noises, trains, floor squeaks, janitors, birds, etc etc.
- make sure the guitar and bass players have changed their strings a day or two ahead of time
- double check the rhythm sections' cabling for hums and have a hard listen to their amps too.
- make sure you have extra reeds, sticks, strings, mutes, picks, etc.
- bullhorn, beer and bar-b-q :)
- determine if there any additional players you'll need to bring in to fill out the sound
- are there players that might need to be replaced (hard call)
This is just a little tiny list..there are an awful lot of considerations under each of these bullets too.
Have you done this before?
BTW - if the choir is straight a capella, I would start there and see how things go. Just my .02