Is it better to trowel the glue so the glue lines are parallel to the long side of the planks or perpendicular, or is it a wash?

It does not matter with wood floor adhesives UNLESS the manufacturer says it does. It is important to use the correct size trowel for the type of floor you are laying according to the adhesive manufacturer's recommendations. And hold the trowel at about a 45 degree angle to the surface you are troweling out.

thanks