Are you experienced at all with recording generally? Not meant as an insult, but the answer will flavor the responses.

Basic setup for a very large ensemble would be six microphones. First would be a center stereo pair of either SDC or LDC depending upon the room in one of several coincident or near coincident stereo techniques-ORTF, NOS, Blumlein, or spaced omni pair. These would be about 6-10 feet behind the conductor and if band or orchestra about three feet above the conductors head pointed down into the front couple of rows of musicians. If this is a choir then point them at the bottom tier of a three tier riser or the second tier of a four tier riser-even with the aiming point of very slightly higher pointed down.

The second pair of microphones would be room mic's and I usually use spaced omni for this and about 10-20' behind the first pair again depending on the room and size of ensemble. This pair I sometimes leave out altogether if the room is very live since that will get picked up by the mains as well. These mic's are what you would use for resonance and reverb unless you happen to own a Bricasti box.

The third pair are usually cardioid but sometimes omni mic's and are called outriggers or various versions of spot mic. Place one two thirds the distance between the main pair and the last arc of musicians. Place the other in the mirror image on the opposite side. These should be about two feet higher than a seated musician and aimed down into the group. You aren't trying to grab the brass or drums in the back. They'll be heard just fine trust me. I only use these on quite large bands and orchestras and never on choirs. These will have to be delayed to match the main stereo pair so step off or tape the distance from the outrigger to the main pair and also the outrigger to the first musician dead ahead. One foot is more or less one millisecond of delay. These are support mics and when mixed are additive and NOT in any way shape or form to be loud enough to be a prominent portion of the mixed sound.

I use variations of the above all the time as location classical recording is my bag. Specific versions of a setup are particular to specific locations and a particular ensemble so ultimately it is very important to be familiar with your various microphones and how they respond to various types of groups/rooms both on axis and off axis. For instance, in several halls I record in I only use a stereo ribbon (Royer SF12) and nothing else. In others like the piano recording I made yesterday, I used the SF12 on the piano and a pair of LDC room mic's in spaced omni to blend in.

Thanks and semper fi
I do have some past (very past) experiences in a studio on both sides of the board;however it's been over 30 years since I've used a mixer and related hardware to record.
Seeing as how I've never recorded on such a large scale as a 130+ piece band along with a chorus this is why I turned to this site for experienced help.
This is the first time the band director/conductor has combined the band and chorus in one performance so i'll be working with vocals and instruments together.

By the way I wasn't in the USMC-I was an enlisted member of the USAF

In the FWIW category, I don't use a mixer at all on location...or very rarely anyway. All the "mixing" on site happens in the box (ITB). If the choir is to be on stage with the band or orchestra and performing simultaneously then you will want to hang or boom pole mic the choir from the stage itself with cardioid microphones. If you can at all beg borrow or rent an Alesis HD24XR for the performance that gives you a lot of peace of mind as far as getting it all multitracked and redundant. I recommend you begin by learning the DAW program Reaper as it is as quick as a Blackbird and as powerful as a Warthog. What mic's are you going to use?

(Thanks for your Service. The best barracks I ever stayed in TDY were AF!)

I usually use one mic each side of stage, one soloist mic, one in the crowd (otherwise the applause sounds half-hearted), track separately, and EQ it to taste afterwards. Usually the room will sound "hollow" on the recording, and you end up reducing recorded frequencies between 500Hz and 4kHz, and boosting the lower bass and upper treble to get a better result. Performances of large ensembles sometimes use an XY pair centre-front behind the conductor's head, elevated. All depends on your room and ensemble size, and how bad the acoustics are.

Normal large ensemble mic techniques would rarely leave out a main stereo pair even with flanks precisely because of the big center hole and no real imaging of the ensemble. Single mic's just don't get the job done for me even if I'm going to sum down to mono for broadcast. By judicious use of mic placement and stereo coincident or near coincident techniques one can either include the room or not as desired. Even a large ensemble can be done with a single stereo pair when done well.

I'll add a bit to John's original post. His guestamates of distances are a good starting point, but the ideal distance of the center pair from the ensemble is dependent on several factors.
(a) The choice of pair. Wider configurations like ORTF can go a bit closer, Blumlein and MS I pull back a bit.
(b) The size of the ensemble. You want the pair to get an even mix, but not be so far back that there is no stereo field.
(c) The quality of the room. If it is bad you want to move as close to the band as you can.

Unfortunately, the factors that tend to take precedence are
(d) Aesthetics. Be prepared for complaints about the look of the mic stands.
(e) Logistics. Hard to put stands in the middle of the seats.
(f) Safety. Bring plenty of gaffer tape to make sure stands and cables are secure.