Should a rough wall be smoothed with mortar before installing tile?
Royal Pain the ars to make that wall smooth and workable.
I would remove the drywall and install 1/2&quot;
Denshield. No need to remove the cabinets. the Denshield will give you a nice solid surface to work with.
Added benefit to this is that while the wall is open you can change the electrical box's to adjustable depth one's, once your tile is on you can adjust the box, by turning a screw, so it is the correct depth.
I would use a White mastic for your semi-translucent glass tile.