Lowering will also impact on the stock swaybars. The H&R ones are formed in such a way in that they will not knock (I believe it hits the subframe). Also your camber will be affected heavily especially at the rear. There is some minor adjustment on the front of the car via the subframe to get the front camber back into alignment (just). The rears though you will need to get adjustable control arms to get the camber back into line. While 2.5 degrees or more of camber looks sweet as and handles nicely, it destroys your tyres in no time.
Cheers,
Trent