So from what I can tell, when I bring a rig in or an object in with .fbx, it automatically points along the Y. Both Blender and Maya are consistent in terms of orientation. Y to Y from Blender and Z to Y from Maya.
The Alembic settings for Blender and Maya also orient it properly. 90 rotation on the X and -1 Y scale.
I have not dug deeply into the math inside Unreal and I am not a programmer. The part that is confusing is the fact that the orthograpic views and the default camera with no rotations point down the X as forward. Or not confusing. But is how the math works.
But even the default mannequin and recent mannequin control rig all face down the Y. It seems to be there is a consistent effort to keep the character animation workflow consistent with external apps, regardless of the other orientations, camera and ortho views.
Just my take on it. And I would think for the most part - from my experience - keeping the characters facing the Y is the way to work. And in my opion the best thing is to keep orientation and build your scenes down the Y with X as side to side just as it is in an external app.
But I work mostly with cinematics. I am not sure if would cause other issues I can’t see from a game development perspective.