Story Mode Requirements: Level 50...
Hard Mode: If you know what you're doing, level 49 epic mods (the ones you get from dailies) are good enough.
Nightmare: Full Columi is recommended.
Hmm. I don't know about that middle one. Might have an awful time staying up for the first boss's burn phase and missing enrage. Not saying it's impossible, but that looks like an awful tough clear. Also, on the rare occasion my guild's brought someone that lightly geared into HMEV, they've needed assistance in the duels. Which isn't a big deal because there were other, better geared players to help nuke the target . But if everyone's right on the edge of being able to finish the duel in time on their own, chances are, someone's not going to be able to pull it off. I mean, you'd be fine on Gharj, the pylons and probably Soa, but there are two other bosses.