I doubt anyone's stuck around to read this very overdue let-me-clear-things-up-FAQ-session author's note but anyway, I've had messages and comments discussing the same topics I've replied to with the same answers each time, so I may as well make it official.
Also, congrats! You've made it through over 100,000 words! I wrote the original story when I was 15 and it wasn't even a third of what I've edited it into now, years later. I hope you'll stick around for the sequel ('The Famous Living Dead').
1) What triggered Frank's aggressive/criminal behaviour?
A little PTSD caused by his parents' death and the shooting was wholly down to seeking revenge.
2) Side-effects of being dead?
Although the deceased can physically move and alter objects, they are not visible to the living and can't be heard, touched, etcetera. Hence why it was so easy for Frank to shoplift. It is rare that they will be aware of their death unless they are told or start to feel the effects of being pushed to 'move on' with their soulmate, but some do know.
3) Explain the whole soulmates thing?
Once two deceased souls have bound (basically confessed their love for each other; cliché, I know), signs that they are both ready to move on start appearing. This includes seeing white lights, losing memory, sleeping more, losing sense of touch, experiencing again how you died (the bullet wounds - blood, stomach pains).
4) How do the dead move on to the other side?
'Pure' souls who haven't committed any wrongs like Gerard are free to pass through the light alone if desired, but 'damned' souls who have sinned like our beloved murdering psychopath protagonist rely on their soulmate to get to the other side through the light.
5) Explain Bob and Ray's situation?
They fell in love with the same person and fought over it so hard it killed them. Ray went into hiding, believing he was still alive yet had killed Bob, while Bob vanished and travelled to forget, eventually learning of his death yet meeting other deceased souls around the world who taught him of the soulmate/other side situation. He originally returned only to get his revenge on Ray, but after recognising Frank and Gerard, he sought justice for them and wished to split them up so Frank would be trapped while Gerard could move on.
6) How did Frank not get to see his parents?
They were soulmates and moved on shortly after dying. I tried to depict them as being strongly in love so it seemed believable. Perhaps Gerard finally got to meet the parents (... I should shut up).
7) Why did Gerard find himself in that particular graveyard?
It's where he and Frank were buried.
8) What happened to Frank?
Well, you'll see what happens if you read the next book. At this point, he's doomed for all of eternity to walk the Earth as a ghost as punishment, and the living can't see him.
9) What happened to Bob?
He rots in hell... No, not really. After regaining consciousness, the others had all left, and he was once again alone in the world.
10) What happened to Gerard?
No doubt the most frequently asked question, and the answer is simply whatever you want. That might seem like the lazy way out but if you really want to know what I envisioned, it was that Gerard passed through to a sort of heaven and spent his time happy and moving on from Frank, perhaps even watching over Mikey.
[Sike. The epilogue will clear things up a little bit and you can read more in the sequel. This was how I left things originally before I edited the book...]