If you’re using groups, and you have sends in them, then it’s best not to touch the group faders since that will definitely change the relationship between the wet/dry signal, and thus the sound of your tracks. This is where VCA faders are useful, since they do not add any routing paths to your signal. They merely act on the volume of the tracks linked to them, even when there’s automation in these tracks.
As for monitor mixes, I suggest you enable the Control Room and use it for that. It’s easier to create them there. Actually, I suggest you use the Control Room anyway since it provides so many benefits besides having the ability to create monitor mixes.
HTH