All healing done to you, via your self or others. It really is underrated I think.Vampiric Blood--is that 50% more healing on you? Or just your personal spells?
When I've used Blood to tank I don't take Nec but I do take Blood Gorged. BG is worth it for the expertise at least.
As far as Death strike I'm not sure if it hurts your threat but I don't think you get any benefit from it's heal. I tend to drop them on occasion just to help out the healer.
As far as spec I'd lean more towards this.
Like you though I'm not sure about the Ebon bug. Have thought about going unholy but we already have one and this bug is keeping me from that. We have 2 blood dks and an unholy, I'm frost which I like but also fits in with the guild.