Taking ideas from how other sites are put together is as old as the web itself. Google wasn’t exactly a unique idea, but a copy of a unique idea done much better. That didn’t come out exactly right, but I think the point is made.
However, don’t even start down the road of simply copying an entire site from someone else, that’s known as scraping and will get you no money in the end.
As to your original question, conversion is the key, so you have to strike a balance between quality traffic and the content you have on your site. If you have both of those right, a couple hundred unique visitors a day would be enough for you to quite the day job. Plan on taking a couple of years to get it right tho.