It's pretty simple. The more impressions you can get the more clicks you can get, the more money you can earn. To get more impressions you can do two things. Create more ad space or get more visitors. Neither involve tweaking the ads. One involves creating more pages, the other marketing. So I'd stop asking a million questions and keep building content and keep marketing. Read teh theory, find out the practicalities for yourself.
Yerp, when you get to the stage your site is optimized well, and has an OK income, you can either keep building up that site adding new content, or start on others