Will this wing maintain stability at highway speeds?

Yes. FRP construction is rigid enough to handle aerodynamic loads at speed. Confirm that all mounting points are torqued according to your vehicle's service manual and that the panel is properly seated on the deck before driving.

What are the mounting hole patterns for this wing?

Reference your vehicle's OEM rear deck and spoiler attachment points. Most rear wings use factory drilling locations; verify your deck's hole spacing matches this panel before final installation to avoid unnecessary drilling.

Does the trunk lid close without interference from this spoiler?

That depends on spoiler height and your deck height relative to the trunk opening. Before mounting, dry-fit the wing in position and manually test trunk operation through its full range. Adjust as needed to clear the lid cleanly.