"simplest things", ha?
I don't really know why you want to do it this way?
#1. When I tried to use both a track control for volume and an envelope there is a fight between these - since you normally have envelope in trim/read mode - master is envelope and what you try to do with fader will do nothing since it's reading the envelope.
#2. If you want to control volume both on a number of tracks and a master on top of these - I would:
a) create track folder for master
b) create children tracks that send their stuff to master/parent.
Then you can control volume as you like on children and get an overall master volume on folder track.
Maybe I just don't see what you want to accomplish.
It seems your thinking is to control everything by midi - but you could just as well do this with the audio parts. Soooo much simpler.
To get a snowball kind of effect with the CC7 going from one track to another, controlling still another - you really don't need that.
Think audio.