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Don't worry about Google and pagerank. Or at least: Never write a page for the sake of pagerank. Write articles because you want to write them and feel competent to do it and think that they are needed on your website.
Organize your website in a natural way that benefits your visitors. If your subject is a rather limited one this may mean that you actually do not need many pages. Then it might be a good idea to create other websites about related matters rather than enlargening your original website in a way that might not seem quite natural.