There's so many different ways you can set this up, it's mind boggling... You can:
1. Have an always on OD so that it crunches up when you dig in, the cleans up when you pick softly. The next can be your distortion and the third can be the lead sound.
2. Same as above but run A-B as your lead sound and the third as a volume boost for solos.
And so on. I think it's worthwhile to have fairly different types of distortion for the various stages, so that you've got a lot of different tones to work with. In my church rig I have a Dredge Tone (TS9ish) set really clean for basic tone, a Zendrive set crunchy for my regular rhythm, a Mosferatu set distorted for higher gain, and all 3 on together for a smooth, singing lead... I run into a clean Vox with a volume pedal in line so I can control the lead volume (since, with all that compression, changing guitar volume does nothing to overall volume).