Yep, follow the sound.
Since you start in the software, set it to 0dB there first. Too high in a digital world means trouble right away.
Then gain on your external mixer. Next to the channel faders, these are used throughout a gig, imho. I ALWAYS drop somewhere at a third of the track in a loud spot and check the gain. some tracks are louder than others. Even running things through Platinum Notes, I always check gain.
Then with a track gained 0DB average you set your controller master volume to 0dB. I usually mark this point (bit of white stagetape and a pen will do the trick), as I don’t usually start of at the highest possible volume.
Then the input gain of a PA mixer if applicable and if you are allowed to touch it. Otherwise just tell the house engineer you are “0dB across the board” and he will set it accordingly for you.
Now you can use the channel faders for mixing (keeping in mind the stuff about channel gain) and start with your controllers master at the volume level you want to start with. You an turn that up a bit as the night progresses, but never beyond the little mark you set for 0dB master output.
Presto!