1. When you are working on characters or bits of plot, how
much do you research them? For example, if a character’s profession
played a major
role, would you feel compelled to learn everything you can about profession?
2. How far should a writer try to flesh out a character? I feel like in order for my characters to be real (at least to me), I need whole life stories on them. Is that necessary or even useful?
Your questions are very timely, because I’m currently deciding whether to take on a project set in a very dangerous part of Africa. I love the idea of the movie and the filmmakers involved, so the focus of my decision process is whether I feel I could write the movie without physically going to the region. I would classify myself as moderately adventurous, but I have no interest in catching malaria or being shot in the head, both of which would be (remote) possibilities if I were to travel there. And yet I love to write on location, so I would probably go if given the chance.
On one hand, the idea of first-hand experience is a little silly. George Lucas has never been in space, and even though James Cameron became an expert on the Titanic, his movie was much more concerned with the love story he invented.
But there’s a lot to be said for research in pursuit of verisimilitude. Imagine if Dr. Carter on E.R. referred to "that tube thing-y." Most of the show’s writers aren’t medical doctors, just as the "Sopranos" writers aren’t Mafia, but they’ve all learned enough of the appropriate lingo so that we believe the characters really know what they’re talking about.
When fleshing out your characters, that level of detail should be your goal. You don’t need to know everything, just enough to firmly place them in the world.