Suggestions needed on setup for BMW

Im geting rid of my 95 Celica and have just purchased a used 2001 BMW 325i. My current setup im taking out of my Celica is a Kenwood 4 channel amp powering 6.5" Boston Acoustics, two 12" Memphis powered by a Soundstream amp, and an Alpine CDA-9856 cd deck.

Question 1 - Will this all fit and work correctly in the BMW?

Question 2 - Would it be wise to get a capacitor?

Last question - Will the volume and track buttons on the steering wheel still work properly without the factory cd player (and with my setup)?

Thanks for any help, a BMW is a new thing for me and im trying to do my best not to screw it up.