Tear out the walls to the studs. No greenboard, use 1/2" cbu. If you aren't going to tile all the way to the ceiling, you can stop the cbu about 6" above the showerhead and put in drywall. Figure a place where that last row of tile can bridge the cbu to drywall so it is easier to make the paint look good. Depending on the tile (thickness) you use, you may want to shim the studs out to compensate for the plastered walls you have. Behind the cbu, put us either 6mil plastic sheeting or roofing felt to act as a vapor barrier. Run this down over the lip of the tub and cut it off after you get the cbu up. Leave an 1/8-1/4" gap between the top of the tub and the bottom edge of the cbu. Leave the tile up about 1/8" inch and caulk that joint after finished with the grout. If you have insulation in the walls and it has a vapor barrier, slash it to compromise it - two vapor barriers is not a good thing.
www.johnbridge.com is a great place to ask tiling questions. Here is a great place for HVAC and plumbing issues - we do pretty well on other things as well, but why not go to the tiling experts?