Are your characters fixed or have they changed during the process of writing?
Each of my characters do undergo a transformation throughout the story. The arrogant lawyer who represents people he knows are guilty, the smarmy reporter who is absolutely sure he knows what the truth is even as he lies to cover it up. The cop that wants to do things by the book and then wonders who in the Hell wrote that damn book. I have a back story to each of my characters, even the minor ones. One in particular shows up at the beginning of Fair Play on one paragraph and returns in The Perfect Day as a major character. So yes they change, some more radically than others.
Has working as a Ghost Writer given you a grounding for your own work?
Absolutely! In working as a ghost-writer whether for a fiction book or a television show you are given an overall arc of where the 'writer' wants the story to go. You fill in the details. As a ghost-writer I have written thrillers, romance and a few other genres I'd like to forget. The advantage to ghost writing is that you get paid, usually immediately after the work is done. The disadvantage is that you can't tell anyone that THAT BOOK or TV SHOW was inspired by your work. To date