Recording a choir and recording a band are going to be two TOTALLY different animals. I'll
address the choir archival recording aspect first....... You'll want at least a pair of mics. Placement will be determined by what is available at your
venue. On a stand in the balcony might not be the best option as you'll get a lot of the sound of the room. This could end up being a good thing, but if your room (or that spot in the balcony) doesn't sound great then neither will your recording. The only real way to choose a position is to listen at various places in the room. This includes every axis: X, Y, and Z (height). As far as mic selection goes, for the most part you get what you pay for. If you buy a pair of $100 mics then your recording will sound like it. You have to decide what it's worth to you, considering what the purpose of the recording is.
Now, once you have your main pair of mics set up where they sound the best you may find that you'll need to spot mic the various sections. Maybe the tenor section is weak and the main pair is not picking them up; having a spot mic on that section will allow you to bring more of that in as needed. On the other
hand, maybe you are going for accurately reproducing what is heard in the room. In that case spot mics may not be necessary, however, know that accuracy does not always equal "best" sound.
Now for how to actually capture the audio: Since you have an M7 there are several ways you can
track the audio. The simplest will be to use a pair of mix outs to
send to the recorder of your preference. Mix 1 will be left, Mix 2 right. If you're just using a pair of mics then it's really simple:
send mic one of your stereo pair to Mix 1 and mic 2 to Mix 2. This will give you a hard panned stereo
image and is the most basic way of capturing the performance. If you are adding spot mics then you'll want to mix those in as needed, using both mixes evenly for center placement, or you can
send more to Mix 1 or Mix 2 in order to place those spots in the appropriate place in the stereo
image. What media do you need the recording to be on when you
hand it over? Whatever you use as a recorder, remember that you're going to be operating at
line level (if you're using the M7CL as front end).
For mic suggestions it really just depends on your budget. I would probably start with something like a pair of Neumann KM184's, but that might be beyond your budget. Don't go cheap here, if it's worth doing then it's worth doing right.
Oh, I just saw that you want the judges remarks recorded as well. Are they miked for the PA
system? If so you can just add them into the mix. If not then you'll need to mic them, preferably individually in order to get their comments to tape.