I heard once that characters in books can be nowhere near as complex as people really are. So where is the line drawn between developing characteristics for your characters? Does any special characteristic (such as let's say likes to chew gum or something) have to have some relevant impact on the overall story? Is more allowance given for main characters as opposed to minor characters?
This is a multi-part question, so in true Buried Editor style I shall answer them in my own particular order.
First off, you wanted to know if more allowance is given for main characters as opposed to minor characters? Yes. They are the most important people in the book, so they get the most words. This means you can expand their characterization.
The other two questions are a set wanting to know just how far your characterization can go and if specific characteristics need to do double duty like a scene. At heart here is the difference between details and significant details. As writers, we all know that the easiest way to make our stories believable is to add details, lots and lots of details. After all, as a kid you were much better able to get away with a lie if you had enough convincing details to back it up. However, in writing, every word counts. You still need the details, but they need to be significant.
A good example would be the details in a Nancy Drew book. She’s fourteen (or eighteen depending on the edition), blonde, and drives a blue roadster. Now, some of those details are important. Some of them are not. Ultimately these are subjective, but here is my important. Important details: Age and Nancy can drive and has a car. Unimportant: Blonde and blue roadster. So why are the first two important? We need to know her age so we can tell if her actions are mature or immature. We need to know she can drive and has a car, or it doesn’t make sense how she can wander around town solving mysteries. The fact that she is blonde is unimportant. She wouldn’t act any different if she dyed her hair brunette. And who cares that her car is a blue roadster? It could be a purple VW Bug and still serve the same purpose.
Is there a way for insignificant details to become significant? Sure, if they serve a purpose. One purpose is to differentiate characters from one another. It can be useful to know Nancy is blond if it means that then we can pick her out in a crowd. A roadster is important if it shows Nancy’s social status or material wealth. Character tics like chewing gum can help identify one boy from another.
So use those details, but like everything else, make sure these details have a point.