I've run 45 vs. 65 with minis and no mass-combat cheats, so this is nothing. :D Seriously, 34 combatants is about 1/3 my maximum brainpower limit for figures on a map.

As for what Wen does, that's up to Wen. She has to balance "shoot early, take out a definite threat, but warn the mobsters that the MI5 guys have allies and have spotted them, which means no further surprise" against "hold fire until the mobsters are in contact, maximize surprise, but risk them taking an early shot."