1) it seems you are in fact stealthed for 3 seconds - this doesn't mean you cannot be seen/targeted, they can see/target you if you're too near like now.
2) When it procs, it leaves a debuff on target, and while the debuff is up each damage you deal will heal you for 10% of the damage dealt. I need more tests to see if the debuff stays up easily or drops often.
3) it doesn't give any additional benefit apart the blink
4) it has its own DR; it can be predictable and dispellable, but keep in mind that shiv applies 3 stack of it
5) yes, it still costs energy - but it has a better DPE than mutilate, so when it procs, you should use it.
6) too soon to say this. We don't have good and long bosses to test well the sustained damage of specs. Also, rotations can change a lot depending on what talents you get.
7) it seems so. from what i have received, every rogue says that they have more energy regen than before - anyway it could be a bug and totally unintended.