I don't think there is a certain volume you have to play at, but in my experience , you need to be louder than the noise made by the audience or you end up being background music. It's good that people at the back can still hear the band clearly, but you don't want folk down the front to be uncomfortable. The sound of drum and bass at a good volume is good to hear but you have to compromise to some extent. I find that after a while, our ears become used to the noise and start filtering out certain frequencies and you struggle to hear. It's easy to fall in to the trap of turning up to combat this, when in fact, the sound out front has not changed at all.the real secret is to have a low stage volume and let the pa do the work.
As for mic'ing up drums in small venues. We have to do this in our local, because the volume of the punters is immense and acoustic drums get lost.