Do I meet the edge of tiles with the edge of the actual OPENING/HOLE of an electrical outlet or the edge of the electrical outlet PLATE COVER?
To the edge of the box. You will need to bring the outlet out (by loosening the screws) a little bit, so you can get the plate back on.
Your cover plate needs to cover the edge of the tiles. The electrical box (according to the NEC) must be completely in the field of tiles, or completely out of the tiles. You, according to code, can not split the box between tile and untiled surfaces. Back butter your tiles(apply mastic directly to the back). Put on the first row, plumb and level. Let them dry overnight. Come back and finish your tiling with a straight first row and your chalk line is a non-issue.
