cut down 11x14 and you get two test strips. You get 3 from a 16x20 sheet. Make paper stops from mount board and hinge them with tape and flip them up,down, The other way is a permanent stop at say 12 " and then make pieces 2,3, or what you need to get proper location.

There are safe lights for color.

Rotary cutters are very nice, but they tend to have a plastic pressure strip next to the cut. Color paper unprocessed is sensitive to scratches and the plastic will scratch. You will not see them until the print is finished.