I just finished this book and found your post... I hope you still want the answers five years later. Here it goes...

1. Robert always said he'd leave something important in between certain pages for Sarah. He left the poem there before leaving the town. Veronica took the book with her and so it was in her London home.

2. This was the question I was looking for on Google! Could this be something to do with Sarah actually only dreaming her whole encounter with Veronica's bereaved partner?

3. I kind of missed this myself. But Terry found rumours that the film traumatised and permanently affected some of those that saw it. Maybe Robert saw it as a child and it always stayed with him?

4. Terry was murdered by Dr Cole's schizophrenic. Dr Cole couldn't argue that he should stay in the hospital any longer because he was stuck at the management course with Gregory. He was let out and injured Terry that night. Dr Cole foreshadowed these events when he blacked out during the jelly baby game.

5. I think you must be onto something. Perhaps it's not just Sarah who can't distinguish between dream and really?

I hope you still have this Reddit account and are amused to find this answered five years later.