See my other solutions for this game for general tips for these achievements. I was able to get this goal with 238 idols. (Though I did the 'Long Haul' goal first, so maybe it's possible with fewer idols.)
Additional notes: the Holy Hand Grenade is at the right tip of the triangle formation, and if it is destroyed, your entire team is killed. The other two tips of the triangle are also occupied by monks, so equipping Khouri in the middle is a good choice.