Odd. I thought that the recommendation was 1.25" total after reading in several places that (primarily the official Hardi FAQ for use of 1/4 inch Hardi board to back tile), but now everything I read says 5/8 inch is necessary. There is much documentation of me citing the 1.25" requirement scattered around in forums and e-mails I have records of, but all sources mentioned in any conversation seem to corroborate 5/8 inch requirement now.
My floor is apparently 1.25" so it is no problem. I am used to facts changing.
You cannot turn a room into a pool; you can prevent water from immediately soaking through and finding its way to things it can damage. Given time, the situation may resolve itself if the flow is cut off; or you may need to intervene and remove some of the water.
My utilities come through the walls, not the floor. Was going to bring drain, water, vacuum, and electricity through the floor for the dishwasher; but we are extending a wall here to back that, so utility will come through that.
I always remove cabinets to lay tile. Cabinets are placed on top of tile floor. Pantry will be integral to structure and built before flooring, secured to the subfloor.
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.