Looking at the pictures of your wheels Id say your offsets all wrong. Standard astra is ET48, you can get away with ET40, but yours look more like ET35 and to be honest it dosent matter what you do now, there gonna rub when lowered. I have ET35 on mine with 8" wide rims and by grinding the arch lip right down and fitting irmscher rear bumper brackets I just get away with it. The coupe has slightly bigger arches than a hatch, so for me the best bet is to see if anyone can scim the hubs down on you alloys 5mm or so to the right offset or change em.
