[Dueller]

I'm not trek, but mastic is not normally used in areas where moisture may be a problem. You'll use Thinset...mix it yourself...don't buy in tubs/buckets.. Moisture resistant board for sure on the tub/shower surround...I've used regular in other areas of the bathroom. Seal the grout well. Rough finish of the drywall joints is fine but I would joint compountd/tape, i.e., you don'y have to have a mirrror smooth painted finish under the tile...unless you're using translucent glass tiles...then you'll need a consisitent color coat.

In your tub surround it is likely that it will be slanting towards the drarin...your first coursewill likely have ti be cut so the upper edge is level to continue upwards. Also, consider stopping the tile before you reach the ceiling...if its not perfectly level it will look crappy if you go all the way up. Tiling all the walls all the way up makes it feel like a prison cell...I'd recommend just around the tub and shower just for aesthetic purposes.