Hi,
normally it should not be an issue to add the xenon at this stage. To my opinon you should choose the full set up including high beam assist and adaptive headlights. With this set up in a F31 I drive a car with the best lights ever in my live.
Attached an additonal link for you where you can spend some of your waiting time ;-) i know that it contains not the right engine, but the rest should be useful.
http://www.loaditup.de/files/799457_qbmhwbzguw.pdf
Regards from bavaria to austria.