Properly waterproofing a shower area sharing a living room wall
The proper installation order: vapor barrier, backer-board, tile.



Secondly, since this isn't a drywall/wood wall, the backer-board would protrude the tiles off the wall about 1/2 an inch, this is easily fixed at the top where there is a tile moulding but was wondering if there were any other elegant solutions?

I'm not sure that I understand this problem, but perhaps you need to run the backerboard to the top and corners of the wall. Use tile trim or bullnosed tile along the edges and in the corners anywhere it's necessary.



Thirdly, wouldn't the backer-board cause something similar to https://www.youtube.com/watch?v=5tl1-4FaxUU @ 32:32 with the backerboard and the plaster?

That's drywall in the video, not backer board. The difference is like the difference between cement and chalk. Backer board is cement-like. Drywall (gypsum) is more chalk-like.