Mixing with midi-originated drum tracks, and drum bus question

I always turn midi into audio as a matter of practice. Without that there's always the temptation to keep editing. It helps to mix audio. Midi is part of the creative arranging process. The rendering to audio can be likened to the recoding stage which has to occur before you mix. Sure there'll be small edits if you pick up a mistake but at that stage it's likely I'd use Drum Replacer now that it's available.

I apply this personal rule not only to drums but to all midi. Mixing in audio keeps that process in the one medium.

And yes, send all your drums to a bus. I mix the drums by themselves and once I'm generally happy I can use the bus fader for mixing with the rest of the audio. I tend to mix the kick and snare drums along with crash cymbals first when I work out the dynamics of the whole piece once I have those strong percussive elements sitting correct in relation to one another then it's time to listen to all the drums on their own and mix them before proceeding with the rest of the piece. Of course that's the way I learned and I'm used to doing that. You may find something that suits you more. But it's a place to start when confronted by maybe a dozen or more drum tracks without counting all the other tracks sometimes as many as a hundred or more.