This is a user forum mate, so no one here will have tried SiC yet to give you accurate info. Best contact Carpro global with that particular question. Odds are it's fine to use essence as a base, but it is really critical that you get heat into essence when polishing if it's used as a primer. It could cause issues with longevity of the coating if it does not bond well. They say no to apply by hand, but that likely would extend to a soft pad application and wipe off without really getting it worked in to the panel.
Personally I think carpro coatings are so good, it's just best to use a polish that leaves nothing behind at all (like carpro fixer) and apply the coating to a clean, bare panel. It's not worth it IMO to put a long life coating over a sort live AIO polish. Essence on its own is a brilliant product though.