This Defiantly is scary when you first read over the achievement but there is actually an easy way to do it!
I recommend going into any of the CO-OP Mission, from there Grind 4,000 points for a Hero/villain then go on a killing spree of bots. Rinse and Repeat this method until the achievement pops.
Best heroes are defiantly ranged due to the bots somehow turning into aim gods at close range and they all group up well so its hard to kill everything with a lightsaber but if you prefer melee heroes it wont slow down the prosses. I highly recommend Captain Phasma because she is just amazing at slaying bots and she has health regen.
Good luck and go and Murder some bots!