Yes, that notch is something you definitely want there. It works as a dampener to prevent wheel wobbles at high speed. Not sure if you’ve noticed yet or not but you basically never turn the bars that much and you can turn the scooter just by leaning alone. Almost every accident on a scooter I’ve seen is because somebody turned too sharp.
My disc brakes did not rub when I assembled it. Maybe they were bent a little bit during shipping? Or they just need a tuneup at your local shop.
Yes, the wires are a mess up front. Get some fabric cable ties to try and manage it better. Mine would only catch when I was walking it and I have to turn extremely sharp to get around hallway corners or some thing. They will never catch while you’re riding it since you almost never turn the bars enough for it to do that.