Hi Mr Kent

I would say the blue line is OK. You don't really want thin weak hair at the sides of your piece, because it makes blending more difficult, but at the back and t should be OK.

I wouldn't go to a barber unless you have checked that he knows how to cut in a hairpiece. It is not the same as doing an ordinary haircut - that is the point the guy on the video is making - you don't want hard lines in the cut which will show up as your biohair grows out. Better to find someone who has experience. It doesn't really matter whether he attaches the piece or you do it beforehand, except that you probably don't want to go in bald and have him attach your piece unless he has a private room.

Good luck with the transition.