Thank you!
1. Yes. "/spartanui popup off" - It's not a toggle like some addons. It does require the second ARG.
2. The left backdrop is actually the container frame/backdrop for Bar5. You can't turn it off. However, you can turn on the GRID to make it show that there is actually something there. Go into Interface Options --> Advanced Options and select the "Always Show ActionBars" check box to turn on the Action Bar Grid.
In Vanilla WoW there aren't 6 Action Bars like there is in Burning Crusade and beyond so I had to do something on the right side. Hence the larger blank box which is great for things like a damage meter.
*NOTE* I just checked the popup feature... for some reason the popup off isn't working. It briefly flashes open then immediately closes. So something is closing them back down. I'll have to check the code. I don't recall making any changes to that function so for now it's a bug.