Honestly, this might be the easiest "platnium" assignment. I found it near impossible for me to not beat this.
The keys are as always kill every enemy yourself. Unless you're using engage abusively you'll find your squad is near worthless. I found it useful to use the grenade launch often, trying to kill multiple people at a time. You can earn up to a thousand points easily with good multiple kills.
I beat this level the first time with at least 7000 points with out trying that hard.
After you finish the deck, there's still two more rooms of enemies, approximetly 7 of them, so if you're close press on, and just be careful in those rooms.