Will these skirts block access to my jack points?

No. These rocker panel skirts are designed to clear factory jack point locations. You'll still have access to lift the vehicle with a floor jack or jack stands at the OEM points.

Do these sit lower to the ground than stock rockers?

They mount at the same height as your factory rocker panels. Ground clearance remains unchanged; there's no lower stance effect from these skirts.

How vulnerable is FRP to road debris and curb rash?

FRP is more impact-resistant than some plastics but not indestructible. Heavy curb strikes or debris can crack or chip it. Once damage occurs, that panel section cannot be easily repaired—you'll need to repaint or replace the piece.