1) Figure the best box to check here is 'Lapsed Christian'. My granddaddy was one of those fire and brimstone preachers always scaring people into believing they were bound for Hell unless they lived a very specific kind of life. Myself, my mama and her people, we're born necromancers so as you can probably imagine, it raised one heck of a ruckus in the family.
2) Death is heart stops, no pulse. Most time spirits are dead but you get the occasional coma person projecting but it's usually an extranatural, not a natural.
3) Well that one time when I was ten there was a light and not much else. Before I could get too close they finally pulled me back. The other time with the possession it was just dark but I was sharing a body with a demon. The 'Light' has some legs to it but no one ever says what's beyond it when they're resurrected temporarily. Like they forget. The ones bound for downstairs? Plenty to tell you about screaming and torture and all that.
4) I should probably know the answer to that and I don't want to. Plenty of people I would not like to see reborn.