Too many sites: Too hard. Too few sites: Too hard. You have to find the sweet spot to earn good money.
This is surely a numbers game. The plan sounds reasonable, but none of us have the discipline to carry it through.
One reason why it is hard to make alot of moeny is because google keeps changing thier ranking algos and maintaing and adding conent to a site is alot of work.
There are many people out there with hundreds of websites and they keep them updated by getting freelancers to do work for them, obviously there will have been a stage where they were working flat out for months on their own until they managed to fund it. Then there are people who make one site and profit from it immensely, the guy who created plentyoffish.com is rolling in adsense cash because so many people visit his site.
I have been writing articles lately that target only the highest paying keywords relating to my site and the payout from Google has been abysmal. I mean it's ridiculously low.
So are thousands of others. Are you enjoying what you are writing about though? You will write much better about subjects if you have a real passion for them.
i think it would be hard to take care of all 500 sites, you would have to hire someone and by that time, hosting would cost you a pretty penny aswell .
Be easier if you had 137 pages earning $2 a day , what the article states is stating the obvious, it just puts in a more realistic perspective and well, it looks easier, although it's not, to achieve.