I'd consider checking out the Fairuse policy for videos. If you sit and watch a video and use it in this way without cutting it professionally and editing in reactions, you can quite easily get landed with a copyright lawsuit.

And I don't mean to shoot you down with your project because it's not my intention. Everyone does reaction videos. It's not the best 'niche' to be in and definitely not on Youtube, why don't you upload to Dtube?

Youtube sucks.