How fast is this car?? And few other things?
Absolutely not. This sounds like a purpose built car. I have a feeling daily driving was not that purpose. Let go through your criteria again:
1) how fast is this car? - you answered that already. Scary fast.
2) is 12,200 bucks a good buy? - on first impressions, yes. When you think about it, no. a 700hp twin turbo engine's life span is not very long. especially when this is going to be a daily driven car. That fact that you provided exact information on this cars 1/4 times and speed are a testiment to how hard this car has already been driven. Be prepared for a engine rebuild that costs about as much as the car did.
3) No way in hell is this a good first car. Get a car that you can actually drive within the cars capability. This car is downright irresponsible to buy at a young age. You are likey to hurt yourself or others trying to go faster that you know how to go.
4) gas mileage is not going to be good anywhere. You will need to use at least 93 octane at all times, or risk blowing up the engine. Pair expensive fuel with sub 20mpg and you might as well be driving a motorhome.
Trust me dude, get a sport compact car and enjoy performance driving that you, or your parents, can afford. That mustang may seem temtping but it is stupid. it is obviously a racecar and not smething intended for daily driving. The clutch is probably miserable is heavy traffic too..