To answer your questions:
- The amount of impressions you get has no affect on your earnings.
- Earnings/click are based on the niche of your website, as well as the location of the person clicking.
- When placing more than 1 ad on a page, the best-paying ads are placed on the top. So if you had two ads, and I clicked the lower one, it would get you less money than the higher one. Regarding amount of ads - you want to put as many ads as your website can nicely hold. You want to make the most out of each page, but don't ad spam.