As I had to be aware of the possibility of using RPG Maker or RPG Toolkit in the end, I take it for the main character a parallel common event would be sufficient: if any movement key pressed, player graphic = xwalk.png
However I wasn't sure about NPCs and whether I'd have to include a step switching between move/idle pose throughout move commands when pausing. Needed a framework I could use for them. One possibility was as Robotacon said - non-identical idle poses.
That said, if I keep starting off on the wrong foot, doing things incorrectly, it'll take me forever to make progress... I am so OVER doing things incorrectly.

Will ignore silly ideas of engine constraints from now on.
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Thank you again for your edit, Robatacon. All the walk animations I've found online were profiles only - and I had no idea how to properly foreshorten that. I keep mis-interpreting hips - they always seem to look the opposite to how they are to me. Will get the GF to walk for me and wait for either a DOH or EUREKA moment.
I have no idea what I'd be doing if I was to not mirror the frames. I thought movement in the human body like so was, well, symmetrical.