Find a suitable space. There can be more than 14 different instruments in a symphony orchestra, and it's likely that there will be more than one of each. This situation calls for a recording space that has two important characteristics: space and good acoustics. Recording studios that have sufficiently large live-rooms are likely to be extremely expensive. Reduce the expense by recording on location. The symphony orchestra's regular rehearsal or performance space makes an ideal alternative and mitigates the need to transport the orchestra and all its instruments.
Arrange a three-hour recording session. Contact the booking manager at the rehearsal hall or church to discuss suitable times. You may get a cheaper rate at night.
Organize microphone placement. Visit the recording space before the session and plan where to place the microphones. Measure the distance from where you plan to position your mixing console and the farthest away mic so you know how much cable to bring. When recording an orchestra and chorus, treat the two entities as individual instruments. Recording each instrument and vocalist individually as you would a pop band is needlessly complicated. To capture the essence of a large ensemble, record the sum of the parts.
Set up your mobile recording device. Open a new session and create a new channel for each microphone you intend to use. Double-click on the channel strip to edit the name of each channel. Use abbreviations to minimize clutter on your screen--for example, rather than writing "woodwind microphone 1," write "w.wind 1." Depending on the make and model of the audio interface, this will call for either a FireWire or USB cable.
Place at least three dynamic microphones two meters in front of the orchestra to pick up the "room" sound. Place two dynamic microphones two meters in front of each section to give you options when mixing. Place three microphones one meter in front of the chorus. It needs to be closer because the voices are quieter than the instruments.
Run a sound-check. Have the chorus and each section of the orchestra play their parts separately. As they do, monitor the meter on each channel strip. If the meter "clips," a red light will flash. Decrease the gain on the channel if it clips. Once you've sound-checked each section, run an ensemble sound-check and monitor the channels assigned to the "room."
Record at least three takes. This approach provides the option to take the best bits from each take. If an otherwise good take is ruined by one or two mistakes, cut and past a mistake-free section from another take to create a composite.