Couple things to add on. First, my Titan void abilities did count for stage 3. My very last acolyte was killed with a melee. Second, for stage 1 thralls, I did it at the hand of crota room. It's around 15 thralls that spawn there, so it won't finish it on its own, but still a good chunk. Just hop on one of the computer things and they can't touch you. Third, Urzok the Hated will also spawn during the enemy assaults (when it says "the enemy are moving against each other"). Just remember, Urzok is built like a public event target. His shields will fully recharge in the time it takes to reload most weapons and has a ton of health, so the more, the merrier for taking him down. Plus, the mission afterward is fun. I was playing hopscotch with those green circles on the ground by the end of it, lol. And I can confirm you do not get the white rarity weapon that eventually upgrades into Necrochasm from this too. Nice guide though, I did it my own way, but this is very clear.