Building a surround and am surrounded by questions.

It's for a very small stove. It is five feet high, the surround, and it's cement board over studs faced with ceramic tile. Picture this in the corner of a room, katy-corner with the room walls forming the wings and a three-foot wide specifically-built wall covering the span and forming the back of the surround. Tile is going up 4'. The remainder of the height is being formed from multiple layers of joint compound, over the cement board, bringing the finished 'plastered' wall even with the tile thickness, thus no bull-nose nor transition strip. Is there a question here or am I just running on? Both. What do I use 'tween tile and plaster, something pliable I'm guessing, like a thin bead of caulk. Am I guessing right? Do you you even care. I think if this weren't my post I wouldn't. Nevertheless, your task, if you choose to take it, is to jam an answer through the ether pronto since I plan on doing this this afternoon and Damariscotta Hardware closes at 2. Thank ye all.

(Begreen will arrive here shortly asking if I put spacers between the studs and the cement board and I did sort of but not really and will get to that in a subsequent post because I have to go now because I think I smell something burning.)