how hard is this plan?

It's called MFA & it's a bad idea that was drove into the ground by the masses a couple of years ago.

I mean if your providing quality content whats the big deal?

Researching a niche, finding a good domain, registering it or buying from an auction, ordering hosting, setting up / cloning a CMS/website, configuring everything... and doing that 100 times. When you're at that point, start finding/buying/writing content... and you probably want to have at least 10 articles for each of your sites. So indeed, it's going to take some time and work.

Amount of upkeep depends on your model, but usually there's some. And some x 100 is a crap ton.

As Yukon pointed out, it's very hard to do this profitably on English search. So vast majority of that work might be wasted. I'd rather be very selective and research those niches carefully.

Added: sorry, but "quality content" has lost all meaning on this forum. Unless you've got an article to show us, nobody is going to take that too seriously. And even if you had truly quality content it just might get buried under the avalanche of crap.

yeah your right. probably not even worth it haha

The idea of multiple MFA sites was all the rage up to a few years ago but it just won't work now. The chances are that your AdSense account will be banned by Google way before you get there. You can trust me on this as I had over 1000 sites at one time.