1) Corrosive Mine is definitely an increase anyway you look at it with multiple targets stacked together, so moving in and playing a melee role if possible definitely helps. I never said you do it often in raids, but where they are multiple targets who can be effected by it, it is very very helpful.
2) In the video I get a total of 2 Cull crits on the last 2 Culls I did, so energy ran out. When I parse this spec it is all Cull Crit dependent, so I push my energy praying I will get the proper Crit on Cull I need to pass the parse (parsing hero's FTW).
3) You REALLY need the 4 piece set bonus for this spec to even be playable in my opinion. Using these high energy moves without it is absolutely unplayable and I wouldn't recommend using abilities like EP and LT+Snipe. But again, you NEED that 4 piece for this spec to play properly & efficiently.
4) I am in BiS 186's and I've seen very high parses with 143 crit all the way to 340 crit rating. The higher the crit rating, the more likely your Cull can crit, which can regen your energy. Not having the 4 piece it may help to run more crit to try and get some of the energy you're losing from the 1/2 cost Takedown.