How to know if I have water damage

I've got a contractor doing this work, but really like the great advice I get here. I've got questions on the 'right' way to do some things. I've gotten referrals from friends on this contractor, but have loads of self doubt / wondering if we are doing things different than the other people and want to avoid problems down the road (I'd have gone much simpler in the design but my wife wanted fancier things... We're doing a bath redo - took it down to the studs, custom shower, etc. They are putting up the wonder board (concrete board). They used greenboard from 5' up in the shower and all in the bathroom (only the shower will be tiled). I would have thought wonderboard all the way in the shower but they say that the upper areas of the shower aren't getting wet. Your thoughts? A bigger issue - I picked up 3 triangles of quartz from the company that will do the vanity countertop later. These 3 triangles are supposed to be shelves in the shower. 2 are 3/4" thick and not all that heavy. another that my wife wants as a foot shelf to put her foot on when shaving is heavy - 1 1/8" thicker and larger dimensions. I was asking the supplier and they talked about cutting into the wonderboard / studs. They mentioned how they don't like when people use silicone caulk against the wonderboard (no cutting of the wonderboard / notching the studs. This thing weighs too much on its own for me to think that would be viable but they say it works but doesn't support enough weight. How would you install a corner shelf? These are flat surface pieces of quartz. So while I would think you want it pitched to drain water, the bottles would slide off. But if they are horizontal / any pitch towards the wall, the water will be up against the grout / wall and if not work its way into the wall, will be more prone to mold? Am I overthinking all this? I am of the 'keep it simple' mindset. I'd have the bottles of shampoo on the floor and a wooden stool for shaving / putting her foot up. Is that foot shelf / seat too thick? Are there 'standards' on the height for the foot shelf? and the other shelves? THANKS!

I am remodeling my bathroom, and have removed the original tile. Underneath, adhered to the plywood subfloor, is mortar, and what looks to be mesh tape, possibly glued down. I am removing as much as I can with a chisel, but a good portion is still stuck. I am going[ATTACH]65551[/ATTACH] to be applying Ditra over the subfloor, and I was wondering how thoroughly that mortar and mesh needs to be removed. Will leaving any, even if fairly flat, impact the tile when I place that over the Ditra? Thanks in advance for any help.[ATTACH]65550[/ATTACH]