Of those, I'd use tigerseal. I hate it when people use self tappers, I've even seen people use wood screws ffs.

If it were me tho, I'd fit rivnuts into the sills so you could secure it properly and remove without having to cut/rebond everytime. But only if i had faith the sill had the strength (tho if it didnt have the strength to support a skirt then I'd be addressing that anyway).

Its a modification, therefore insurance should be made aware. Reality is its probably a 50/50 split on whether people inform their insurers on adding a kit, but is it worth having your insurance invalidated for the sake of a couple of bumpers and skirts if you do stack it, or get crashed into..