I always like to work top to bottom, for mess containment reasons, so on a recent bathroom I did drywall, then beadboard, then tile.

Xedos - these details are really key for anyone not wanting the tile edging to be the showcase in the shower or bathroom renovation. I think tile men have grown used to them as a crutch and now that people are learning that with more planning and better design they can be eliminated. When tile profile edging needs to be used I much prefer to look and feel of Butech's Pro Parts. Chrome plated brass! I'm using some now to frame a frameless Kerdi Line Drain installation. Part of a steam shower build here in West Vancouver. In the picture below you can see the two strips installed on top of the Kerdi Line grate. The kerdi was removed from the top with ease and the double sided glue tape cleaned off. Then the green material was installed - that is Laticrete's Hydro Ban Sheet membrane. Look at the shine on the sides! Butech Pro Part

We'll I'm no expert, but I'd probably just paint over the area with hydroban and then set my tile with thinset. Or if you want, a very thin skim of thinset over the rough areas, then the hydroban, then tile with thinset. Now where the tile will join the painted surface I would make sure I had a nice finish on the drywall to accept the paint. I'd want this nice wall area to begin under the last row of tile so that no hydroban shows or rough surface shows.

Having the same issue in my bathroom adjacent to bedroom with a paint treatment I want to not have to redo. There is a leak going on that only happens when shower used. Luckily drained to unfinished area of basement. I will be cutting into drywall to do repair. No way would I mess with tile unless there was no other way. I am going to carefully cut drywall and when repairing hole have a access panel in case of future need. I will find something decorative to go over panel or a furniture piece, bookshelf or high dresser.