/fa/ - Fashion

So I am thinking of getting an undercut. I don't know how good the barber will be, so I want to know as much as I can myself. I think the parts circled in red are too long (reason for the shave around), and the wavey lines are where the last person left the hair a little longer to blend. So I'm going to go a 1 most likely around, leave the top intact, but how high should I make the shave? Never had an undercut before so hoping for the best here. idk what all to tell the person