Warlock advice needed

I recently started playing GD (got a bit side tracked by other games).
And I decideded roll an warlock.

Right now I am working out a build that is focusing DEE and Doombolt.

With curse of frailty and fammiliar + mend flesh for support. Arcanist mastery just for the passives.

I have some questions,

I wondering if I should max out the DEE line, Does terrifying gaze and vile eruption make a huge difference? Or will the damage output be enough with blood burst maxed?

I was also wondering if Sigil of consumption with destruction are worth my while? I was thinking the life leech might not work on bosses, however it will work on trash, and quite alot of bosses summon trash mobs.

I have some other general questions
does energy leech work with skills (DEE) or do I have to use auto attacks?
How does vitality and chaos damage hold up in ultimate? As in which mobs are highly resistant to it?

thank you in advance.