It's probably just HP damage (per round). Some official 4E article said how wierd it was that warforged DR was applying to poison damage.
Weird, but could be simply the -5 penalty for being distracted. Spot must have been a typo.
That probably just points out that it's a humanoid whose soul and body are indistinguishable. Other outsiders probably will be immortal beasts, immortal elementals (or perhaps immortal oozes?)...
Shouldn't be much different from devilsight.
That's because it is not a regular ranged attack, but a special attack. If it were, it would be listed as Ranged in bold, instead of Spine Rain in bold. It's a standard action and has range of 10 squares. What I do NOT get is the "+9 Dex".