You’ll recall the discussion we had in this thread:
This shows my master rack, which contains my typical master chain. Among this:
- EQ for both of my separate outputs
- Automated master volume for each output
- a master limiter for each output (to avoid distortion when pushing levels too far up)
Also, it contains a separate LUFS meter for each output. I only use these for setting up levels in the studio, but of course you could also use any metering plugin and display it when playing live. You could even create a binding to show the metering GUI at the touch of a button on your keyboard/controller
This master rack needs to be included in every individual song file, since no audio connections to the background rack are available.
TBH, I have little use for metering when playing live - I tend to set my levels when creating songs, so that everything is under control, nice and tidy. Then I simply need to watch my master volume fader - as long as that one is pretty much centered, no need to worry about levels. And my other volume meter is on pretty much all the time: my in-ear monitors! When levels get too high, I get a splitting headache 
Cheers,
Torsten