Should my character face y-forward? I've been using Blender for years. Before when I pushed NUM 1 I would be looking at the character's face. CTRL NUM 1 would show me his back. It worked for me, and never mattered in the larger scheme of things.

Question: Have I been doing it wrong? Is Positive Y the direction the character must face?
those shortcuts activate view alignment modes named "front" and "back" 



so I can't see why you feel they could be wrong, even if those are just names, and you can choose whatever (even to work not aligned to anything, but of course it helps...)

that said, some symmetry related tool considers the default (sometimes the only possible) symmetry around X axis, so that the object shape is considered mirrored on the +Y and -Y axis

This is clearly the case of "humanoid" features (like a face) so it seems to be considered the best choice, imho.