Direction of wood planks

your instincts are correct. there's no standard way.

how about diagonal? haha

My first thought was diagonal, as well, but I wonder if once you put the furniture in place if the floor boards will really make that much difference.

go for concrete flooring with prints of skulls, that's the fashionable thing these days

Some say it should be perpendicular to the main bank of windows, so the light streaming across it doesn't accentuate minor height differences and other imperfections. But I've mostly seen it parallel to the long walls of the LR.

The linearity that bothers you in an empty room won't be noticeable once you clutter it up with crap. I'm not sure if that's correct design jargon, though.