i think you are wasting your time focusing on the building of the sites as opposed to the marketing. If you build one quality website that gets very popular it will far exceed the profits of 500 small time websites. I am not trying to knock your plan but it has been done by many many people already. You can see in websites for sale how cheap you can get premade adsense niche content sites, as opposed to how expensive i mean literally the amount of value for one popular website that has a large market control.
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