Not sure about the code issues.
@UNBREAKABLE.
My guess which is completely non educated, running common ground back to panel, and securing metal boxes to red iron would be fiiiiinnnnnneee. Lol.
I seriously have no clue.
I don't see the logical difference securing surface mount boxes to the red iron, and having the emt clamped and secured to the red iron as it runs to panel.
Definitely 3v and 5v would be easier as more large flat area of no corrugated to trim out around the box. You could then put all terminations and boxes where the flat areas of tin would be.