How Much Is Too Much?
As I alluded to in a previous post, a friend once stated that I should have the entire background of every major and minor character in any story I write. I, of course, thought this ludicrous because it would mean I'd spend more time digging into the background of a character than writing their three lines of dialog. So, of course, I don't write that way. For most of my characters that are important to the story, I have basic facts like age, a general description (if it's important), where they were born. Really, I have details of each character if I actually state it o ruse it in the story. But if the details aren't important because it's an ancillary character, I have no details. Now, this is what I do, but should you do the same?
What Works For You
One of the ways to determine what works for you is to try things simply. First, try just to have a few blurbs of a biography of a character and then move on from there. If that doesn't work, like it feels you're writing with an empty character, then try adding more. You can even go so far and to give their entire backgrou8nd like my friend mentioned. You can have where they went to college, high school, grade school, and even kindergarten. You can have their favorite subjects, their GPA, their friends names. You have a multi-page dossier on each character. You can even hop onto Google and find a random picture of a person that looks like the person you are doing this for. If that helps you write better, then so be it!
At rare times when I'm coming up with the idea for a book and need to dig a little more, I will find pictures that remind me of it. But that picture isn't just used in a simple manner. I sometimes find a picture of something similar to what I have in mind for scenery. Then I can utilize that picture to describe the scenery a little better. When I was writing The Reader of Books series, I was consulting bus schedules as well as various city maps when the character traveled. When I started writing The Silver Brothers: The Last Stand, I was consulting old maps to see where roads existed and where they didn't between Washington, D.C., and Montana. When I was starting writing the second book in the series, The Silver Brothers: The Lodestone, I had to know how the character got from Ohio over to Montana. So that meant digging up maps of railroads from the 1870s. That meant looking at what types of major roads existed. That meant knowing what train stations looked like during that time. I had a few pictures that helped me describe them. So that worked out pretty well.
So my point for this entry is that you only need to go as far as you need to know the background of a character or the scenery that you choose. You only have to go into the details enough to help you write. While you can go deeper, you don't necessarily have to.