rather the being a jack of all traits you'll be the master of one. concentrating on one genre. then marketing, link building and trafficking will be much easier.
A niche is also refered to as a "small group of people who are searching online for the solution to a very SPECIFIC problem". Find that group, make sure you'll face little or no competition catering to that group, create the product that solves their problem, and then you're sure you'll make money when you launch your business online. Why? The search engines will easily pick you up as the expert in your field (also a definition of niche), and rank you high in the search engine results the next time the people in that small group (the "market") you're targeting do their search with their credit cards in their hands.
have a site that you are passionate to do.. don't worry about google adsense.. they will come later.. as soon as you create enough traffic to convert... and use also reliable affiliates, it will drive ur income higher hope that helps