Hi, I am looking to go for a run as pure evil.

I am thinking, turn vampire and dark brotherhood. Side with Stormcoaks as they seem the worst. Any other ideas what routes to take. I have exhausted the theifs guild so I am not looking for that.

Sounds good, but maybe some acts of mass murder in the smaller settlements eg. Morthal, Ivarstead, Shors Stone, Riverwood etc?

Killing innocents isnt evil. In such a hard world liberating people from it would be a kindness. Nonono.

Enslave, deceive and control. That is how you make them bend the knee, one by one. Killing people may extinguish light from their eyes, but it is a short term fulfillment. Break up lovers and families, send their children to the mines as you watch the parents despair, place the seeds of betrayal and gain power through ambition to control the population through terror so everytime their heart beats - it beats of fear and sadness. When they are broken and throw themselves on their own blade - then you have succeeded.

If you want truly amoral, seek out the bulk of the Deadric quests. All deal in murder, betrayal, corruption, degradation, sadism.
Avoid Meridia, as she is one of the few Daedra who isn't evil.
The Thieves Guild might suit you as well for that "Just in it for the money" angle.
Dark Brotherhood is a given.

No need. Get her "holy" blade and use it for acts of evil. Slaughter innocents with it and pervert her name through corruption.

Well you could, yeah, but it seems to defeat the purpose. From a roleplaying point of view, despite the fact that she'll give the quest to anybody, she has a hardon again undead and evil things-- so she probably wouldn't bestow her honor...Or she'd take it away from you once you displeased her. They can do that, you know.

But they won't, right?