Yeah it appears I need to farm Dreadful Essences from the boss himself...that takes alot of time. So to get him to 4 stacks I would need to get three Essences first. 30min respawn inbetween each one...
On top of that we would only then have 1 shot to down him at 4 stacks then he would go back down to one.
No, the stacks stay on him once you apply them. If you wipe, wait 5 min and try again.
That being said, DON'T put more on then you can handle, you have no way of getting them off