What do you mean with "in real time"?
A man on a mixer has two hands to level the output in real time...
A comp/limiter will give you a static output level and you can use one for each instrument.
A noisegate is useful for eleminate surrounding noises of the microphones (drums and singer).
If you need some special effects like reverb/delay/flange then they should be controlled by the drummer itself (like the effects of a guitarist/keyboardist).