There is not a foam pad equivalent to wool. The coarsest foam pads I've used are the yellow from Chemical Guys. They cut really well, but not as good as wool. Finished to 5000, you should be able to start with foam, but if you did not completely remove the scratches each step the foam will not remove them. I just use wool initially because it removes the scratches with 1 pass, then go to orange foam CG pad with compound to refine the scratches. As AAE suggested, wipe your panel with 710 or isopropyl alcohol after compounding to make sure sand scratches are completely gone before going to next step.