For ARC i believe you might only use Bloodbath from MRD. And you can always use skull sunder and maim on any job. Its great to have regardless of classes (maim deals more damage at my THM than my nukes lol) since these 2 skills are the pearls of this classe.

I'd suggest defender too, but for ARC having skills that lower attack isn't really nice. For crossclass skill, i'd suggest you to look for GLA skills. Rampart, Still precision, Cadence, Obsess and some other skills wuld be great too have as ARC.