Brabus will lower it approx. an inch.
1. No rubbing/interference in the front, will make it look 100X's better, 17" will have an aggressive stance, barely any wheel gap, ideal IMHO. My 19"s raise it an inch, back to OEM height w/o the fugly fender gap. It'll look like this, sorry for the dark and bad pics, cheap digital camera.
2. Very very similar, you will not notice the difference. Springs are good enough, if it wears the shocks in a few years, get the whole coilover system, that's what I'm planning to do.
You will love the new look and feel.