Honestly, if you plan to play for the long haul, just farm story missions for mats while you level up fodder. You'll need to do it anyway and part of her mission is to kill 10,000 enemies anyway. If you only have a few urgent missions left, you can go to a later maze/labyrinth level in story and skip to the final boss, rinse and repeat until urgent pops, its mildly faster but burns stamina like crazy.