Transferring anchor locations from the wall to plywood
IMO, the most accurate would be to create a template out of a lighter material, maybe builders paper, the thick brown paper that comes in rolls.  Create a piece the exact size of the ply, tape two together if necessary.  

Tape it up on the wall, mark the edges and then the stud mounting points.  Move the paper to the ply and drill your pilot holes.  Hold the board up to the wall, match up your marks and then fasten away.

The sequence may not match your fastener type, but I hope you get my point. 

I think this is the most surefire way to guard against oddly spaced and non-plumb studs.