If someone were to buy the 2 qi per win booster, would they be able to gain 200 qi per day as opposed to 100? Or is the 100qi limit concrete?

I'm pretty sure the 100 qi in 24 hours limit is set in stone.
So as opposed to playing 100 games to get 100 qi, playing 50 games with the qi booster should net you 100 qi. The booster only serves to speed things along.

Don't quote me on this, but I believe the cap for gaining qi and tc is 100 games a day. Meaning you would be able to get 200 qi a day at max while using this booster.