Depends really, my mates small bumper 8v was pristine under the strips once we took them off, just needed a clean. If the car has had paint before then look closely, often the strips are left on the car which would result in a nasty line where they used to be.
Oh and apart from the obvious, you need the sill fitting kit. this comes with a load of clips and fixings necessary to attach it all to the car. I believe GSF sell these kits?