Ok. Suspension/drivetrain is something you want to do right the first time. I would advise doing a lot more research before you proceed with any of this, based on the questions you're asking.
The standard sport suspension in the 3-series is decent; I would not modify it for the sake of modifying it. If your goal is to simply adjust the height of the car and make the ride firmer/more complaint, then coilovers are a good bet. Search here to see what people are using ..... KW V1 is popular, I have no experience with them however.
2011 BMW 335i - 6MT, M Sport, Le Mans blue, Logic7