Sanding wood Worktop

Morning, All

Happy Sunday.

My kitchen working is in desperate need to sanding and applying a new coating. For this, I usually use Rustins Plastic Coating.

Looking at my currently worktop, there are lots of marks, scratches etc and I also need to remove the current coating.

What coarse sandpaper is best to prep the worktop? I will be using my Random Orbital Sander to do this.

Thanks,
Mark