Posting frequency is unrelated to blog earnings. Post as much or as little as you want. Some people could post once a month and get $500, while others could post 500 times a month and make $1.
Yeap absolutely, the amount of money you earn depends a lot on the popularity of your blog, instead of thinking about money, first try to put good and unique content in your blog and to promote your blog aggressively. Who knows one day, 1 post can earn you $500. But that will need a lot of hard work.
Why content is the king? Content = the key to get more attention from SE Content = the key to get more attention from public Content = traffic
Post extremely good, no matter even if you post once a week. Along with creating king content, market your blog very well, so that it can earn, else I'm not sure if content alone can make a success!