I can't help with Driver Assist Plus, but have a 2014 X3 28i with M-Sport.
I don't believe M-Sport changes the suspension, but you're right in that it does add 19" wheels, which may result in a slightly courser ride. I haven't noticed.
I have DHP, which I assume you'll be getting as well since you said most all options and packages. I highly recommend it. In Comfort (default) mode, the ride is VERY compliant, but it still handles decently. In Sport mode, I still find it comfortable enough, and it handles MUCH better. I spend about 80% of time in comfort mode and find it very cushy. No long trips yet, but so far, very happy. I would say you will have no regrets on MSport if you have DHP. I'd bet it would be fine without DHP, too, but I just can't comment since it isn't the way my car is configured.
Good luck! Great car, whatever you choose.