Cheers.

Is there an ideal width for cleats?  2" seems to be popular on YouTube.

I've used cdx ply for the walls of several shops. Depending on the thickness, you can screw things right to it without needing to find a stud. I've painted it un sanded and it looks fine, (to me ). You only need to sand it for esthetic reasons. The amount of work it would take to make a measurable difference in the finish you might be better off buying shop grade or presanded one side.