Sheet rock meets plaster wall

Brick wall with plaster meets a (green) wall board.
(If this topic sounds a bit familiar, I've posted in the past week on this. Now I'm trying to get a refinement on what I should do...)
Do I put a thin layer of plaster on the brick wall to fill in little scratches, etc., before doing the corner? Must *all* paint and wallpaper glue (the paper is off the wall) be removed from the plaster before adding another coat of plaster?
Do I use joint compound and tape at the corner on both the wall board *and* the plaster wall? Taper from the corner 10-12 inches on both?
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