I don’t think you should have any issues with adhesion, as long as the epoxy is clean and dry. I find using denatured alcohol works well for this purpose.
I would still take it to at least 600 grit, if not 800-1000. I don’t think epoxy is very forgiving when it comes to showing sanding marks or scratches. If you want a super glossy finish, like the epoxy looks right after pouring/drying, I have had the best results with automotive 2K clear coat out of an airbrush. Even car wax and a buffer wheel was still too dull looking. Also, using this automotive clear coat, I have only needed to sand up to 600 because the clear coat fills in most if not all of the small scratches. I posted about using this here: https://forum.onefinitycnc.com/t/anyone-had-experience-wet-sanding-to-poloshing-epoxy/16777/2