Gain before feedback is cut in half each time you double the number of open mics. Eliminate microphones by using direct feeds from instrument amplifiers, keyboards, etc. Use equalization to control feedback as a last resort. Position speakers and microphones to reduce the potential for feedback. A 1000Hz sound wave is only about a foot long, so moving a microphone, speaker, or monitor just an inch or two may solve your problem without touching your equalizer.
Microphones reject sound from certain directions for a reason.
Minimize the use of stage monitors when possible. Users can adjust their own volume levels while eliminating unnecessary stage volume that clutters the sound in the seating area. Your sound system must be operated about 25dB SPL louder than the ambient noise in the room for best intelligibility and clarity. An average sound pressure level of 125dB is, for the most part, impossible to attain, so it makes sense that the monitor volume in the room needs to be reduced in order to improve the clarity of the system for the audience. If you wear ear plugs when playing, turn down the volume.