Edit: Might as well use the Envy skull as well for maximum easitude, it makes it so that the chief gets the Arbiter's cloak ability, so you can just waltz into an area, see where the enemies are and then blow them straight to hell. Also the Bandanna skull, for infinite ammo. It says the zero multipliers "disable achievements" but that applies to the level completion/par achievements, and not to the "do X in this level."
The scarab skull makes this achievement a lot easier. Enable the skull and any weapon you're using shoots the scarab gun ammo, and anything downrange of you is gonna' die in a few shots. Even vehicles will crumble with only a short burst. Weapons will still have their same fire rate and ammo usage so the weapons I recommend using are a rapid fire weapon (plasma rifle or SMG) and a 2x zoom rifle, preferably a Battle Rifle because of the 3-round burst but a Carbine will work as well. You start off with an SMG and can grab a Battle Rifle off one of the unfortunate Helljumpers that landed further up the hill and died.
If you're just going for this achievement then I'd definitely suggest doing it on Heroic, mainly because of all the beam rifle jackals. While it's still not that bad on Legendary having to face beam rifle jackals means if they shoot you then you'll die and go back to checkpoint, whereas on Heroic a shot from a beam rifle jackal just drops your shields.
For the most part the level is open enough that you can just shoot the enemies, but even with parts that are a bit cramped usually just shooting the wall behind the enemies will kill them quickly without hurting you. Also melee attacks and grenades work as normal so if you're having issues in cramped areas use them.