Distance from edge of wood at buttpad to rear sling stud: Longer than the bottom butt pad screw. Typically 1.5"-2 1/2" is an aesthetically pleasing range.
Distance of forward sling stud: An aesthetic proportion might be 2x the rear dimension, measured from the tip, or perhaps the visual center of the tip if it's angled.
Every job is easy with the right tools. The B-Square Sling Swivel Stud Installation Kit is a collection of all the right tools.
Put masking tape tightly worked into the wood over the area to prevent splitting.