A flat, empty surface serving as a podium. 4 x 3 m minimum.
Overhead lights for the Orchestra to be able to read the scores.
If the OPSO is to use the piano, it would need to be tuned to 440 Hz (not higher).
A secure dressing room for the musicians. A separate dressing room for the singer if available.
The Orchestra never uses microphones except for the singer's voice, which is carried through an adequate amplifier brought by the singer. In that case the Orchestra would need the host to provide a power cord with a 220 V plug on the podium.