Bmw 118i lci 2017 b38

[kahlon]

Hello guys, I need some help with my bmw, so one of the things are that whenever I brake, or whenever I drive the car the car wants to go left and I just want to know what it could be like the steering will want to go left i dont know if its alignment or what.
And secondly it actually consumes so much fuel for a 1.5litre, it has a exhaust leak but it consumes alot any ideas why, I have to fill it up like every few days to be honest. I filled it up about 2 days ago and it was more than half a tank of fuel now its gone down to like 1 bar left on it, it had 260 miles on the tank something like that now its gone to 80miles.
Another thing is I want to go stage 1 for this car for more power and better fuel efficiency and alot of people are telling it will be too much stress on the engine or whatever and that I cant do it, I want to do alot to this car I know it wont be able to stage 2 because the engine wont be able to handle it its a b38, but it has to be able to go stage 1 because i really do want to put a decat and intake on it, anyone who knows or has done the same? Just need help with these problems.