It's not meant to be scale! John's working on a scale one, but this is the cartoon one. I'll definitely be building the scale air tractor when it comes out, but for now I'm really enjoying my ft duster - it's a fast and simple build and is very fun to fly.
For the red lines on plans I cut partway with a knife (pretty shallow) and then drag on old gift card or plastic hotel key through it. That's more of a 90% cut. To score the inside folds for the airfoil I just cut the paper then drag the tip of a bbq skewer through it.