Hi Ian!
I’d say a guitar behaves a bit different than a piano in that every struck (or tapped/picked/etc) note will be more different than a piano who uses a felted hammer to strike the string(s).
If you have the time (and patience) try and sample at least every second note.
Three round robins is great so is two to three velocity layers.
I’d sample a soft and medium/hard and a super loud layer and then have the loudest layer only on velocity 127.
Best of luck!
/Anders
