I am working on a story right now and I realised I hadn't been spending enough time developing my characters, but the trouble is that now I don't know how long I should be spending doing it. I've only spent about 100 words each introducing and developing two characters. Is this enough to simply bring the reader's awareness to their existence - their name, and a little backstory? The characters will be key in the story, but they won't be appearing for a while yet (another few thousand words). Thanks in advance!