Make sure to not use VE during the normal phases and only use it in the intermissions if possible. If you're unlucky you get chain-silenced and might die.
The intermissions in the kill were probably the unluckiest I ever survived, without VE I would've died there for sure.
Most of my attempts ended up hitting the berserk (on my first good attempt I had berserk on 27%), try to get only 3 horrors in P1, if you get a 4th its probably not possible anymore. You can also use the necrotic plague (Fade -> Shadowfiend in the right moment) but then horrors in the start might live very long and you might have to run more than I did.
I actually did utilise necrotic plague in my first kill and went with insanity instead of FDCL. Of course at the time my ilvl was 547 and felt that using FDCL and manually killing the horrors took too long
Also coulda sworn there was a thread on this just recently.
Indeed they might live longer than usual but it didnt really matter how long they lived as long as they are kited all the time. The plague will kill them eventually. The plague doesn't always dodge the horrors, only reason they seem to live long is that at the beginning, when the plague stack is still low, they can easily survive it. The only other random issue is when the plague falls off completely when an add dies and there were no other adds around to receive it. As long as that doesn't happen, plague can be a good source of damage on adds, and lets you focus more on the boss.
Having Insanity will make transition phases easier, and it was the main reason I used it.